NEWS

New in spot 1.99a (not yet released)

  * Major changes (including backward incompatible changes):

    - The curstomized version of BuDDy (libbdd) used by Spot has be
      renamed as (libbddx) to avoid issues with copies of BuDDy
      already installed on the system.

    - ltlgrind is a new tool that mutates LTL or PSL formulas.  If you
      have a tool that is bogus on some formula that is too large to
      debug, you can use ltlgrind to generate smaller derived formulas
      and see if you can reproduce the bug on those.

    - ltlcross has a new option --grind, that attempts to reduce the
      size of any bogus formula it discovers, while still exhibiting
      the bug.

    - randaut is a new tool that generates random automata.

    - autfilt is a new tool that converts/filters/transforms a
      stream of automata.

    - "ltlfilt --stutter-invariant" will now work with PSL formula.
      The implementation is actually much more efficient
      than the previous implementation that was only for LTL.

    - ltlfilt's old -q/--quiet option has been renamed to
      --ignore-errors.  The new -q/--quiet semantic is the
      same as in grep (and also autfilt): disable all normal
      input, for situtations where only the exit status matters.

    - There is a parser for the HOA format
      (http://adl.github.io/hoaf/) available as a
      spot::hoa_stream_parser object or spot::hoa_parse() function.
      The former version is able to parse a stream of automata, in
      order to do batch processing.  This format can be output by all
      tools (since Spot 1.2.5) using the --hoa option, and it can be
      read by autfilt (by default) and ltlcross (using the %H
      specifier).   The current implementation does not support:
        - acceptance specifications involving "Fin(x)", "|", or "f".
	- alternation
      but the rest is expected to work.  Those restrictions cause the
      automaton to be interpretable as a TGBA.  In particular,
      multiple initial states are converted into an extra initial
      state; complemented acceptance sets Inf(!x) are converted to
      Inf(x); negated (maybe after duplication); explicit or implicit
      labels can be used; aliases are supported; "--ABORT--" can be
      used in a stream.  The parser currently ignore all optional
      headers (starting with a lowercase letter).

    - The above HOA parser can also parse neverclaims, so the
      neverclaim parser has been removed.  This implies that
      autfilt can input a mix of HOA and neverclaims, and that
      ltlcross' %N and %H specifiers (used to indicate whether
      a tool produces neverclaims or HOA) are now synonyms.

    - randomize() is a new algorithm that reorder the states
      and transition of an automaton at random.  It can be
      used from the command-line using "autfilt --randomize".

    - the interface in iface/dve2 has been renamed to iface/ltsmin
      because it can now interface the dynamic libraries created
      either by Divine (as patched by the LTSmin people) or by
      Spins (the LTSmin compiler for Promela).

    - Spot is now compiling in C++11 mode.  The set of features we use
      requires GCC >= 4.6 or Clang >= 3.1.  These minimum versions
      are old enough that it should not be an issue to most people.

    - Boost is not used anymore.

    - The tgba_succ_iterator interface has changed.  Methods next(),
      and first() should now return a bool indicating whether the
      current iteration is valid.

    - The tgba base class has a new method, release_iter(), that can
      be called to five a used iterator back to its automaton.  This
      iterator is then stored in a protected member, iter_cache_, and
      all implementations of succ_iter() can be updated to recycle
      iter_cache_ (if available) instead of allocating a new iterator.

    - The tgba base class has a new method, succ(), to support
      C++11' range-based for loop, and hide all the above change.

      Instead of the following syntax:

	tgba_succ_iterator* i = aut->succ_iter(s);
	for (i->first(); !i->done(); i->next())
	  {
	     // use i->current_state()
	     //     i->current_condition()
	     //     i->current_acceptance_conditions()
	  }
	delete i;

      We now prefer:

	for (auto i: aut->succ(s))
	  {
	    // use i->current_state()
	    //     i->current_condition()
	    //     i->current_acceptance_conditions()
	  }

      And the above syntax is really just syntactic suggar for

	tgba_succ_iterator* i = aut->succ_iter(s);
	if (i->first())
	  do
	    {
	      // use i->current_state()
	      //     i->current_condition()
	      //     i->current_acceptance_conditions()
	    }
	  while (i->next());
	aut->release_iter(i); // allow the automaton to recycle the iterator

      Where the virtual calls to done() and delete have been avoided.

    - tgba::succ_iter() now takes only one argument.  The optional
      global_state and global_automaton arguments have been removed.

    - The following methods have been removed from the TGBA interface and
      all their subclasses:
        - tgba::support_variables()
	- tgba::compute_support_variables()
	- tgba::all_acceptance_conditions()       // use acc().accepting(...)
	- tgba::neg_acceptance_conditions()
	- tgba::number_of_acceptance_conditions() // use acc().num_sets()
      methods have been removed from the TGBA interface and all
      subclasses.

    - Membership to acceptance sets are now stored using bit sets,
      currently limited to 32 bits.  Each TGBA has a acc() method that
      returns a reference to an acceptance object (of type
      spot::acc_cond), able to operate on acceptance marks
      (spot::acc_cond::mark_t).

      Instead of writing
        i->current_acceptance_conditions() == aut->all_acceptance_conditions()
      we now write
        aut->acc().accepting(i->current_acceptance_conditions())

      Similarly,
        aut->number_of_acceptance_conditions()
      is now
        aut->acc().num_sets()


  * Removed features

    - The long unused interface for GreatSPN (or rather, interface to
      a non-public, customized version of GreatSPN) has been removed.
      As a consequence, the we could get rid of many cruft in the
      implementation of Couvreur's FM'99 emptiness check.

    - Support for symbolic, BDD-encoded TGBAs has been removed.  This
      includes the tgba_bdd_concrete class and associated supporting
      classes, as well as the ltl_to_tgba_lacim() LTL translation
      algorithm.  Historically, this TGBA implementation and LTL
      translation were the first to be implemented in Spot (by
      mistake!) and this resulted in many bad design decisions.  In
      practice they were of no use as we only work with explicit
      automata (i.e. not symbolic) in Spot, and those produced by
      these techniques are simply too big.

    - All support for ELTL, i.e., LTL logic extended with operators
      represented by automata have been removed.  It was never used in
      practice because it had no practical user interface, and the
      translation was a purely-based BDD encoding producing huge
      automata (when viewed explictely), using the above and non
      longuer supported tgba_bdd_concrete class.

    - Our implementation of the Kupferman-Vardi complementation has
      been removed: it was useless in practice beause of the size of
      the automata built, and it did not survive the conversion of
      acceptance sets from BDDs to bitsets.

    - Conversion from TGBA to state-based Generalized Büchi automata
      has been removed too, because it was only used by the KV
      complementation.

    - The unused implementation of state-based alternating Büchi automata
      has been removed.

New in spot 1.2.6a (not yet released)

  Nothing yet.

New in spot 1.2.6 (2014-12-06)

  * New features:

    - ltlcross --verbose is a new option to see what is being done

  * Bug fixes:

    - Remove one incorrect simplification rule for PSL discovered
      via checks on random formulaes.  (The bug was very unlikely
      to trigger on non-random formulas, because it requires a SERE
      with an entire subexpression that is unsatisfiable.)
    - When the automaton resulting from the translation of a positive
      formula is deterministic, ltlcross will compute its complement
      to perform additional checks against other translations of the
      positive formula.  The same procedure should be performed with
      automata obtained from negated formulas, but because of a typo
      this was not the case.
    - the neverclaim parser will now diagnose redefinitions of
      state labels.
    - the acceptance specification in the HOA format output have been
      adjusted to match recent changes in the format specifications.
    - atomic propositions are correctly escaped in the HOA output.
    - the build rules for documentation have been made compatible with
      version 8.0 of Org-mode.  (This was only a problem if you build
      from the git repository, or if you want to edit the
      documentation.)
    - recent to changes to libstd++ (as shipped by g++ 4.9.2) have
      demonstrated that the order of transitions output by the
      LTL->TGBA translation used to be dependent on the implementation
      of the STL.  This is now fixed.
    - some developpement version of libstd++ had a bug (PR 63698) in
      the assignment of std::set, and that was triggered in two places
      in Spot.  The workaround (not assigning sets) is actually more
      efficient, so we can consider it as a bug fix, even though
      libstd++ has also been fixed.
    - all parsers would report wrong line numbers while processing
      files with DOS style newlines.
    - add support for SWIG 3.0.

New in spot 1.2.5 (2014-08-21)

  * New features:

    - The online ltl2tgba translator will automatically attempt to
      parse a formula using LBT's syntax if it cannot parse it using
      the normal infix syntax.  It also has an option to display
      formulas using LBT's syntax.

    - ltl2tgba and dstar2tgba have a new experimental option --hoaf to
      output automata in the Hanoï Omega Automaton Format whose
      current draft is at http://adl.github.io/hoaf/
      The corresponding C++ function is spot::hoaf_reachable() in
      tgbaalgos/hoaf.hh.

    - 'randltl 4' is now a shorthand for 'randltl p0 p1 p2 p3'.

    - ltlcross has a new option --save-bogus=FILENAME to save any
      formula for which a problem (other than timeout) was detected
      during translation or using the resulting automatas.

  * Documentation:

    - The man page for ltl2tgba has some new notes and references
      about TGBA and about monitors.

  * Bug fixes:

    - Fix incorrect simplification of promises in the translation
      of the M operator (you may suffer from the bug even if you do
      not use this operator as some LTL patterns are automatically
      reduced to it).
    - Fix simplification of bounded repetition in SERE formulas.
    - Fix incorrect translation of PSL formulas of the form !{f} where
      f is unsatisifable.  A similar bug was fixed for {f} in Spot
      1.1.4, but for some reason it was not fixed for !{f}.
    - Fix parsing of neverclaims produced by Modella.
    - Fix a memory leak in the little-used conversion from
      transition-based alternating automata to tgba.
    - Fix a harmless uninitialized read in BuDDy.
    - When writing to the terminal, ltlcross used to display each
      formula in bright white, to make them stand out.  It turns out
      this was actually hiding the formulas for people using a
      terminal with white background... This version displays formula
      in bright blue instead.
    - 'randltl -n -1 --seed 0' and 'randltl -n -1 --seed 1' used to
      generate nearly the same list of formulas, shifted by one,
      because the PRNG write reset with an incremented seed between
      each output formula.  The PRNG is now reset only once.

New in spot 1.2.4 (2014-05-15)

  * New features:

    - "-B -x degen-lskip" can be used to disable level-skipping in the
      degeralization procedure called by ltl2tgba and dstar2tgba.
      This is mostly meant for running experiments.
    - "-B -x degen-lcache=N" can be used to experiment with different
      type of level caching during degeneralization.

  * Bug fixes:

    - Change the Python bindings to make them compatible with Swig 3.0.
    - "ltl2tgta --ta" could crash in certain conditions due to the
      introduction of a simulation-based reduction after
      degeneralization.
    - Fix four incorrect formula-simplification rules, three were
      related to the factorization of Boolean subformulas in
      operands of the non-length-matching "&" SERE operator, and
      a fourth one could only be enabled by explicitely passing the
      favor_event_univ option to the simplifier (not the default).
    - Fix incorrect translation of the fusion operator (":") in SERE
      such as {xx;1}:yy[*] where the left operand has 1 as tail.

New in spot 1.2.3 (2014-02-11)

  * New features:

    - The SPOT_SATLOG environment variable can be set to a filename to
      obtain statistics about the different iterations of the
      SAT-based minimization.  For an example, see
      http://spot.lip6.fr/userdoc/satmin.html
    - The bench/dtgbasat/ benchmark has been updated to use SPOT_SATLOG
      and record more statistics.
    - The default value for the SPOT_SATSOLVER environment
      variable has been changed to "glucose -verb=0 -model %I >%O".
      This assumes that glucose 3.0 is installed.   For older
      versions of glucose, remove the "-model" option.

  * Bug fixes:

    - More fixes for Python 3 compatibility.
    - Fix calculation of length_boolone(), were 'Xa|b|c' was
      considered as length 6 instead of 4 (because it is 'Xa|(b|a)'
      were (b|a) is Boolean).
    - Fix Clang-3.5 warnings.
    - randltl -S did not honor --boolean-priorities.
    - randltl had trouble generating formulas when all unary, or
      all binary/n-ary operators were disabled.
    - Fix spurious testsuite failure when using Pandas 0.13.
    - Add the time spent in child processes when measuring time
      with the timer class.
    - Fix determinism of the SAT-based minimization encoding.
      (It would sometimes produce different equivalent automata,
      because of a different encoding order.)
    - If the SAT-based minimization is asked for a 10-state automaton
      and returns a 6-state automaton, do not ask for a 9-state
      automaton in the next iteration...
    - Fix some compilation issue with the version of Apple's Clang
      that is installed with MacOS X 10.9.
    - Fix VPATH builds when building from the git repository.
    - Fix UP links in the html documentation for command-line tools.

New in spot 1.2.2 (2014-01-24)

  * Bug fixes:

    - Fix compilation *and* behavior of bitvectors on 32-bit
      architectures.
    - Fix some compilation errors observed using the antique G++ 4.0.1.
    - Fix compatibility with Python 3 in the test suite.
    - Fix a couple of new clang warnings (like "unused private member").
    - Add some missing #includes that are not included indirectly
      when the C++ compiler is in C++11 mode.
    - Fix detection of numbers that are too large in the ELTL parser.
    - Fix a memory leak in the ELTL parser, and avoid some unnecessary
      calls to strlen() at the same time.

New in spot 1.2.1 (2013-12-11)

  * New features:

    - commands for translators specified to ltlcross can now
      be given "short names" to be used in the CSV or JSON output.
      For instance
         ltlcross '{small} ltl2tgba -s --small %f >%N' ...
      will run the command "ltl2tgba -s --small %f >%N", but only
      print "small" in output files.

    - ltlcross' CSV and JSON output now contains two additional
      columns: exit_status and exit_code, used to report failures of
      the translator.  If the translation failed, only the time is
      reported, and the rest of the statistics, which are missing,
      area left empty (in CVS) or null (in JSON).  A new option,
      --omit-missing can be used to remove lines for failed
      translations, and remove these two columns.

    - if ltlcross is used with --products=+5 instead of --products=5
      then the stastics for each of the five products will be output
      separately instead of being averaged.

    - if ltlcross is used with tools that produce deterministic Streett
      or Rabin automata (as specified with %D), then the statistics
      output in CSV or JSON will have some extra columns to report
      the size of these input automata before ltlcross converts them
      into TGBA to perform its regular checks.

    - ltlfilt, ltl2tgba, ltl2tgta, and ltlcross can now read formulas
      from CSV files.  Use option -F FILE/COL to read formulas from
      column COL of FILE.  Use -F FILE/-COL if the first line of
      FILE be ignored.

    - when ltlfilt processes formulas from a CSV file, it will output
      each CSV line whose formula matches the given constraints, with
      the rewriten formula.  The new escape sequence %< (text in
      columns before the formula) and %> (text after) can be used
      with the --format option to alter this output.

    - ltlfile, genltl, randltl, and ltl2tgba have a --csv-escape option
      to help escape formulas in CSV files.

    - Please check
            http://spot.lip6.fr/userdoc/csv.html
      for some discussion and examples of the last few features.

  * Bug fixes:

    - ltlcross' CSV output has been changed to be more RFC 4180
      compliant: it no longuer output useless cosmetic spaces, and
      use double-quotes with proper escaping for strings.  The only
      RFC 4180 rule that it does not follow is that it will terminate
      lines with \n instead of \r\n because the latter cause issues
      with a couple of tools.

    - ltlcross failed to report missing input or output escape sequences
      on all but the first configured translator.

New in spot 1.2 (2013-10-01)

  * Changes to command-line tools:

    - ltlcross has a new option --color to color its output.  It is
      enabled by default when the output is a terminal.

    - ltlcross will give an example of infinite word accepted by the
      two automata when the product between a positive automaton and a
      negative automaton is non-empty.

    - ltlcross can now read the Rabin and Streett automata output by
      ltl2dstar.  This type of output should be specified using '%D':

        ltlcross 'ltl2dstar --ltl2nba=spin:path/to/ltl2tgba@-s %L %D'

      However because Spot only supports Büchi acceptance, these Rabin
      and Streett automata are immediately converted to TGBAs before
      further processing by ltlcross.  This is still interesting to
      search for bugs in translators to Rabin or Streett automata, but
      the statistics (of the resulting TGBAs) might not be very relevant.

    - When ltlcross obtains a deterministic automaton from a
      translator it will now complement this automaton to perform
      additional intersection checks.  This is complementation is done
      only for deterministic automata (because that is cheap) and can
      be disabled with --no-complement.

    - To help with debugging problems detected by ltlcross, the
      environment variables SPOT_TMPDIR and SPOT_TMPKEEP control where
      temporary files are created and if they should be erased.  Read
      the man page of ltlcross for details.

    - There is a new command, named dstar2tgba, that converts a
      deterministic Rabin or Streett automaton (expressed in the
      output format of ltl2dstar) into a TGBA, BA or Monitor.

      In the case of Rabin acceptance, the conversion will output a
      deterministic Büchi automaton if one such automaton exist.  Even
      if no such automaton exists, the conversion will actually
      preserves the determinism of any SCC that can be kept
      deterministic.

      In the case of Streett acceptance, the conversion produces
      non-deterministic Büchi automata with Generalized acceptance.
      These are then degeneralized if requested.

      See http://spot.lip6.fr/userdoc/dstar2tgba.html for some
      examples, and the man page for more reference.

    - The %S escape sequence used by ltl2tgba --stats to display the
      number of SCCs in the output automaton has been renamed to %c.
      This makes it more homogeneous with the --stats option of the
      new dstar2tgba command.

      Additionally, the %p escape can now be used to show whether the
      output automaton is complete, and the %r escape will give the
      number of seconds spent building the output automaton (excluding
      the time spent parsing the input).

    - ltl2tgba, ltl2tgta, and dstar2tgba have a --complete option
      to output complete automata.

    - ltl2tgba, ltl2tgta, and dstar2tgba can use a SAT-solver to
      minimize deterministic automata.  Doing so is only needed on
      properties that are stronger than obligations (for obligations
      our WDBA-minimization procedure will return a minimimal
      deterministic automaton more efficiently) and is disabled by
      default.  See the spot-x(7) man page for documentation about the
      related options: sat-minimize, sat-states, sat-acc, state-based.
      See also http://spot.lip6.fr/userdoc/satmin.html for some
      examples.

    - ltlfilt, genltl, and randltl now have a --latex option to output
      formulas in a way that its easier to embed in a LaTeX document.
      Each operator is output as a command such as \U, \F, etc.
      doc/tl/spotltl.sty gives one possible definition for each macro.

    - ltlfilt, genltl, and randltl have a new --format option to
      indicate how to present the output formula, possibly with
      information about the input.

    - ltlfilt as a new option, --relabel-bool, to abstract independent
      Boolean subformulae as if they were atomic propositions.
      For instance "a & GF(c | d) & b & X(c | d)" would be rewritten
      as "p0 & GF(p1) & Xp1".

  * New functions and classes in the library:

    - dtba_sat_synthetize(): Use a SAT-solver to build an equivalent
      deterministic TBA with a fixed number of states.

    - dtba_sat_minimize(), dtba_sat_minimize_dichotomy(): Iterate
      dtba_sat_synthetize() to reduce the number of states of a TBA.

    - dtgba_sat_synthetize(), dtgba_sat_minimize(),
      dtgba_sat_minimize_dichotomy(): Likewise, for deterministic TGBA.

    - is_complete(): Check whether a TGBA is complete.

    - tgba_complete(): Complete an automaton by adding a sink state
      if needed.

    - dtgba_complement(): Complement a deterministic TGBA.

    - satsolver(): Run an (external) SAT solver, honoring the
      SPOT_SATSOLVER environment variable if set.

    - tba_determinize(): Run a power-set construction, and attempt
      to fix the acceptance simulation to build a deterministic TBA.

    - dstar_parse(): Read a Streett or Rabin automaton in
      ltl2dstar's format.  Note that this format allows only
      deterministic automata.

    - nra_to_nba(): Convert a (possibly non-deterministic) Rabin
      automaton to a non-deterministic Büchi automaton.

    - dra_to_ba(): Convert a deterministic Rabin automaton to a Büchi
      automaton, preserving acceptance in all SCCs where this is possible.

    - nsa_to_tgba(): Convert a (possibly non-deterministic) Streett
      automaton to a non-deterministic TGBA.

    - dstar_to_tgba(): Convert any automaton returned by dstar_parse()
      into a TGBA.

    - build_tgba_mask_keep(): Build a masked TGBA that shows only
      a subset of states of another TGBA.

    - build_tgba_mask_ignore(): Build a masked TGBA that ignore
      a subset of states of another TGBA.

    - class tgba_proxy: Helps writing on-the-fly algorithms that
      delegate most of their methods to the original automaton.

    - class bitvect: A dynamic bit vector implementation.

    - class word: An infinite word, stored as prefix + cycle, with a
      simplify() methods to simplify cycle and prefix in obvious ways.

    - class temporary_file: A temporary file.  Can be instanciated with
      create_tmp_file() or create_open_tmpfile().

    - count_state(): Return the number of states of a TGBA.  Implement
      a couple of specializations for classes where is can be know
      without exploration.

    - to_latex_string(): Output a formula using LaTeX syntax.

    - relabel_bse(): Relabeling of Boolean Sub-Expressions.
      Implements ltlfilt's --relabel-bool option describe above.

  * Noteworthy internal changes:

    - When minimize_obligation() is not given the formula associated
      to the input automaton, but that automaton is deterministic, it
      can still attempt to call minimize_wdba() and check the correcteness
      using dtgba_complement().  This allows dstar2tgba to apply
      WDBA-minimization on deterministic Rabin automata.

    - tgba_reachable_iterator_depth_first has been redesigned to
      effectively perform a DFS.  As a consequence, it does not
      inherit from tgba_reachable_iterator anymore.

    - postproc::set_pref() was used to accept an argument among Any,
      Small or Deterministic.  These can now be combined with Complete
      as Any|Complete, Small|Complete, or Deterministic|Complete.

    - operands of n-ary operators (like & and |) are now ordered so
      that Boolean terms come first.  This speeds up syntactic
      implication checks slightly.  Also, literals are now sorted
      using strverscmp(), so that p5 comes before p12.

    - Syntactic implication checks have been generalized slightly
      (for instance 'a & b & F(a & b)' is now reduced to 'a & b'
      while it was not changed in previous versions).

    - All the parsers implemented in Spot now use the same type to
      store locations.

    - Cleanup of exported symbols

      All symbols in the library now have hidden visibility on ELF systems.
      Public classes and functions have been marked explicitely for export
      with the SPOT_API macro.

      During this massive update, some of functions that should not have
      been made public in the first place have been moved away so that
      they can only be used from the library.  Some old of unused
      functions have been removed.

      removed:
	- class loopless_modular_mixed_radix_gray_code

      hidden:
	- class acc_compl
	- class acceptance_convertor
	- class bdd_allocator
	- class free_list

  * Bug fixes:

    - Degeneralization was not indempotant on automata with an
      accepting initial state that was on a cycle, but without
      self-loop.

    - Configuring with --enable-optimization would reset the value of
      CXXFLAGS.


New in spot 1.1.4 (2013-07-29)

  * Bug fixes:
    - The parser for neverclaim, updated in 1.1.3, would fail to
      parse guards of the form (a) || (b) output by ltl2ba or
      ltl3ba, and would only understand ((a) || (b)).
    - When used from ltlcross, the same parser would fail to
      parse further neverclaims after the first failure.
    - Add a missing newline in some error message of ltlcross.
    - Expressions like {SERE} were wrongly translated and simplified
      for SEREs that accept the empty word: they were wrongly reduced
      to true.  Simplification and translation rules have been fixed,
      and the doc/tl/tl.pdf specifications have been updated to better
      explain that {SERE} has the semantics of a closure operator that
      is not exactly what one could expect after reading the PSL
      standard.
    - Various typos.

New in spot 1.1.3 (2013-07-09)

  * New feature:
    - The neverclaim parser now understands the new style of output
      used by Spin 6.24 and later.
  * Bug fixes:
    - The scc_filter() function could abort with a BDD error.  If all
      the acceptance sets of an SCC but the first one were useless.
    - The script in bench/spin13/ would not work on MacOS X because
      of some non-portable command.
    - A memory corruption in ltlcross.

New in spot 1.1.2 (2013-06-09)

  * Bug fixes:
    - Uninitialized variables in ltlcross (affect the count of terminal
      weak, and strong SCCs).
    - Workaround an old GCC bug to allow compilation with g++ <= 4.5
    - Fix several Doxygen comments so that they display correctly.

New in spot 1.1.1 (2013-05-13):

  * New features:

    - lbtt_reachable(), the function that outputs a TGBA in LBTT's
      format, has a new option to indicate that the TGBA being printed
      is in fact a Büchi automaton.  In this case it outputs an LBTT
      automaton with state-based acceptance.

      The output of the guards has also been changed in two ways:
      1. atomic propositions that do not match p[0-9]+ are always
         double-quoted.  This avoids issues where t or f were used as
         atomic propositions in the formula, output as-is in the
         automaton, and read back as true or false.  Other names that
         correspond to LBT operators would cause problem as well.
      2. formulas that label transitions are now output as
         irredundant-sums-of-products.

    - 'ltl2tgba --ba --lbtt' will now output automata with state-based
      acceptance.  You can use 'ltl2tgba --ba --lbtt=t' to force the
      output of transition-based acceptance like in the previous
      versions.

      Some illustrations of this point and the previous one can be
      found in the man page for ltl2tgba(1).

    - There is a new function scc_filter_states() that removes all
      useless states from a TGBA.  It is actually an abbridged version
      of scc_filter() that does not alter the acceptance conditions of
      the automaton.  scc_filter_state() should be used when
      post-processing TGBAs that actually represent BAs.

    - simulation_sba(), cosimulation_sba(), and
      iterated_simulations_sba() are new functions that apply to TGBAs
      that actually represent BAs.  They preserve the imporant
      property that if a state of the BA is is accepting, the outgoing
      transitions of that state are all accepting in the TGBA that
      represent the BA.  This is something that was not preserved by
      functions cosimultion() and iterated_simulations() as mentionned
      in the bug fixes below.

    - ltlcross has a new option --seed, that makes it possible to
      change the seed used by the random graph generator.

    - ltlcross has a new option --products=N to check the result of
      each translation against N different state spaces, and everage
      the statistics of these N products.  N default to 1; larger
      values increase the chances to detect inconsistencies in the
      translations, and also make the average size of the product
      built against the translated automata a more pertinent
      statistic.

    - bdd_dict::unregister_all_typed_variables() is a new function,
      making it easy to unregister all BDD variables of a given type
      owned by some object.

  * Bug fixes:

    - genltl --gh-r generated the wrong formulas due to a typo.
    - ltlfilt --eventual and --universal were not handled properly.
    - ltlfilt --stutter-invariant would trigger an assert on PSL formulas.
    - ltl2tgba, ltl2tgta, ltlcross, and ltlfilt, would all choke on empty
      lines in a file of formulas.  They now ignore empty lines.
    - The iterated simulation applied on degeneralized TGBA was bogus
      for two reasons: one was that cosimulation was applied using the
      generic cosimulation for TGBA, and the second is that
      SCC-filtering, performed between iterations, was also a
      TGBA-based algorithm.  Both of these algorithms could lose the
      property that if a TGBA represents a BA, all the outgoing
      transitions of a state should be accepting.  As a consequence, some
      formulas where translated to incorrect Büchi automata.

New in spot 1.1 (2013-04-28):

  Several of the new features described below are discribed in

    Tomáš Babiak, Thomas Badie, Alexandre Duret-Lutz, Mojmír
    Křetínský, Jan Strejček: Compositional Approach to Suspension and
    Other Improvements to LTL Translation.  To appear in the
    proceedings of SPIN'13.

  * New features in the library:

    - The postprocessor class now takes an optional option_map
      argument that can be used to specify fine-tuning options, making
      it easier to benchmark different scenarios while developing new
      postprocessings.

    - A new translator class implements a complete translation chain,
      from LTL/PSL to TGBA/BA/Monitor.  It performs pre- and
      post-processings in addition to the core translation, and offers
      an interface similar to that used in the postprocessor class, to
      specify the intent of the translation.

    - The degeneralization algorithm has learned three new tricks:
      level reset, level caching, and SCC-based ordering.  The former
      two are enabled by default.  Benchmarking has shown that the
      latter one does not always have a positive effect, so it is
      disabled by default.  (See SPIN'13 paper.)

    - The scc_filter() function, which removes dead SCCs and also
      simplify acceptance conditions, has learnt how to simplify
      acceptance conditions in a few tricky situations that were not
      simplified previously.  (See SPIN'13 paper.)

    - A new translation, called compsusp(), for "Compositional
      Suspension" is implemented on top of ltl_to_tgba_fm().
      (See SPIN'13 paper.)

    - Some experimental LTL rewriting rules that trie to gather
      suspendable formulas are implemented and can be activated
      with the favor_event_univ option of ltl_simplifier.  As
      always please check doc/tl/tl.tex for the list of rules.

    - An experimental "don't care" (direct) simulation has been
      implemented.  This simulations consider the acceptance
      of out-of-SCC transitions as "don't care".  It is not
      enabled by default because it currently is very slow.

    - remove_x() is a function that take a formula, and rewrite it
      without the X operator.  The rewriting is only correct for
      stutter-insensitive LTL formulas (See K. Etessami's paper in IFP
      vol. 75(6). 2000) This algorithm is accessible from the
      command-line using ltlfilt's --remove-x option.

    - is_stutter_insensitive() takes any LTL formula, and check
      whether it is stutter-insensitive.  This algorithm is accessible
      from the command-line using ltlfilt's --stutter-insensitive
      option.

    - Several functions have been introduced to check the
      strength of an SCC.
        is_inherently_weak_scc()
	is_weak_scc()
	is_syntactic_weak_scc()
	is_complete_scc()
	is_terminal_scc()
	is_syntactic_terminal_scc()

      Beware that the costly is_weak_scc() function introduced in Spot
      1.0, which is based on a cycle enumeration, has been renammed to
      is_inherently_weak_scc() to match established vocabulary.

  * Command-line tools:

    - ltl2tgba and ltl2tgta now honor a new --extra-options (or -x)
      flag to fine-tune the algorithms used.  The available options
      are documented in the spot-x (7) manpage.  For instance use '-x
      comp-susp' to use the afore-mentioned compositional suspension.

    - The output format of 'ltlcross --json' has been changed slightly.
      In a future version we will offer some reporting script that turn
      such JSON output into various tables and graphs, and these change
      are required to make the format usable for other benchmarks (not
      just ltlcross).

    - ltlcross will now count the number of non-accepting, terminal,
      weak, and strong SCCs, as well as the number of terminal, weak,
      and strong automata produced by each tool.

  * Documentation:

    - org-mode files used to generate the documentation about
      command-line tools (shown at http://spot.lip6.fr/userdoc/tools.html)
      is distributed in doc/org/.  The resulting html files are also
      in doc/userdoc/.

  * Web interface:

    - A new "Compositional Suspension" tab has been added to experiment
      with compositional suspension.

  * Benchmarks:

    - See bench/spin13/README for instructions to reproduce our Spin'13
      benchmark for the compositional suspension.

  * Bug fixes:

    - There was a memory leak in the LTL simplification code, that could
      only be triggered when disabling advanced simplifications.

    - The translation of the PSL formula !{xxx} was incorrect when xxx
      simplified to false.

    - Various warnings triggered by new compilers.

New in spot 1.0.2 (2013-03-06):

  * New features:
    - the on-line ltl2tgba.html interface can output deterministic or
      non-deterministic monitors.  However, and unlike the ltl2tgba
      command-line tool, it doesn't different output formats.
    - the class ltl::ltl_simplifier now has an option to rewrite Boolean
      subformulaes as irredundante-sum-of-product during the simplification
      of any LTL/PSL formula.  The service is also available as a method
      ltl_simplifier::boolean_to_isop() that applies this rewriting
      to a Boolean formula and implements a cache.
      ltlfilt as a new option --boolean-to-isop to try to apply the
      above rewriting from the command-line:
      	    % ltlfilt --boolean-to-isop -f 'GF((a->b)&(b->c))'
	    GF((!a & !b) | (b & c))
      This is currently not used anywhere else in the library.
  * Bug fixes:
    - 'ltl2tgba --high' is documented to be the same as 'ltl2tgba',
      but by default ltl2tgba forgot to enable LTL simplifications based
      on language containment, which --high do enable.  There are now
      enabled by default.
    - the on-line ltl2tgba.html interface failed to output monitors,
      testing automata, and generalized testing automata due to two
      issues with the Python bindings.  It also used to display
      Testing Automaton Options when the desired output was set to Monitor.
    - bench/ltl2tgba would not work in a VPATH build.
    - a typo caused some .dir-locals.el configuration parameters to be
      silently ignored by emacs
    - improved Doxygen comments for formula_to_bdd, bdd_to_formula,
      and bdd_dict.
    - src/tgbatest/ltl2tgba (not to be confused with src/bin/ltl2tgba)
      would have a memory leak when passed the conflicting option -M
      and -O.  It probably has many other problems.  Do not use
      src/tgbatest/ltl2tgba if you are not writing a test case for
      Spot.  Use src/bin/ltl2tgba instead.

New in spot 1.0.1 (2013-01-23):

  * Bug fixes:
    - Two executions of the simulation reductions could produce
      two isomorphic automata, but with transitions in a different
      order.
    - ltlcross did not diagnose write errors to temporary files,
      and certain versions of g++ would warn about it.
    - "P0.init" is parsed as an atomic even without the double quotes,
      but it was always output with double quotes.  This version will
      not quote this atomic proposition anymore.
    - "U", "W", "M", "R" were correctly parsed as atomic propositions
      (instead of binary operators) when placed in double quotes, but
      on output they were output without quotes, making the result
      unparsable.
    - the to_lbt_string() functions would always output a trailing space.
      This is not the case anymore.
    - tgba_product::transition_annotation() would segfault when
      called in a product against a Kripke structure.
  * Minor improvements:
    - Four new LTL simplifications rules:
        GF(a|Xb) = GF(a|b)
        GF(a|Fb) = GF(a|b)
        FG(a&Xb) = FG(a&b)
        FG(a&Gb) = FG(a&b)
    - The on-line version of ltl2tgba now displays edge and
      transition counts, just as the ltlcross tool.
    - ltlcross will display the number of timeouts at the end
      of its execution.
    - ltlcross will diagnose tools with missing input or
      output %-sequence before attempting to run any of them.
    - The parser for LBT's prefix-style LTL formulas will now
      read atomic propositions that are not of the form p1, p2...
      This makes it possible to process formulas written in
      ltl2dstar's syntax.
  * Pruning:
    - lbtt has been removed from the distribution.  A copy of the last
      version we distributed is still available at
        http://spot.lip6.fr/dl/lbtt-1.2.1a.tar.gz
      and our test suite will use it if it is installed, but the same
      tests are already performed by ltlcross.
    - the bench/ltl2tgba/ benchmark, that used lbtt to compare various
      LTL-to-Büchi translators, has been updated to use ltlcross.  It
      now output summary tables in LaTeX.  Support for Modella (no
      longer available online), and Wring (requires a too old Perl
      version) have been dropped.
    - the half-baked and underdocumented "Event TGBA" support in
      src/evtgba*/ has been removed, as it was last worked on in 2004.

New in spot 1.0 (2012-10-27):

  * License change: Spot is now distributed using GPL v3+ instead
    of GPL v2+.  This is because we started using some third-party
    files distributed under GPL v3+.

  * Command-line tools

    Useful command-line tools are now installed in addition to the
    library.  Some of these tools were originally written for our test
    suite and had evolved organically into useful programs with crappy
    interfaces: they have now been rewritten with better argument
    parsing, saner defaults, and they come with man pages.

    - genltl:   Generate LTL formulas from scalable patterns.
                This offers 20 patterns so far.

    - randltl:  Generate random LTL/PSL formulas.

    - ltlfilt:  Filter lists of formulas according to several criteria
                (e.g., match only safety formulas that are larger than
		some given size).  Besides being used as a "grep" tool
		for formulas, this can also be used to convert
		files of formulas between different syntaxes, apply
		some simplifications, check whether to formulas are
		equivalent, ...

    - ltl2tgba: Translate LTL/PSL formulas into Büchi automata (TGBA,
                BA, or Monitor).  A fundamental change to the
                interface is that you may now specify the goal of the
                translation: do you you favor deterministic or smaller
                automata?

    - ltl2tgta: Translate LTL/PSL formulas into Testing Automata.

    - ltlcross: Compare the output of translators from LTL/PSL to
                Büchi automata, to find bug or for benchmarking.  This
                is essentially a Spot-based reimplementation of LBTT
                that supports PSL in addition to LTL, and that can
                output more statistics.

    An introduction to these tools can be found on-line at
      http://spot.lip6.fr/userdoc/tools.html

    The former test versions of genltl and randltl have been removed
    from the source tree.  The old version of ltl2tgba with its
    gazillion options is still in src/tgbatest/ and is meant to be
    used for testing only.  Although ltlcross is meant to replace
    LBTT, we are still using both tools in this release; however this
    is likely to be the last release of Spot that redistributes LBTT.

  * New features in the Spot library:

    - Support for various flavors of Testing Automata.

      The flavors are:
      + "classical" Testing Automata, as used for instance by
	Geldenhuys and Hansen (Spin'06), using Büchi and
	livelock acceptance conditions.
      + Generalized Testing Automata, extending the previous
	with multiple Büchi acceptance sets.
      + Transition-based Generalized Testing Automata moving Büchi
        acceptance to transitions, and getting rid of livelock
        acceptance conditions by expliciting stuttering self-loops.

      Supporting algorithms include anything required to run
      the automata-theoretic approach using testing automata:

      + dedicated synchronized product
      + dedicated emptiness-check for TA and GTA, as these
        may require two passes because of the two kinds of
	acceptance, while a TGTA can be checked for emptiness
	with the same one-pass algorithm as a TGBA.
      + conversion from a TGBA to any of the above kind, with
        options to reduce these automata with bisimulation,
	and to produce a BA/GBA that require a single pass
	(at the expense of determinism).
      + output in dot format for display

      A discussion of these automata, part of Ala Eddine BEN SALEM's
      PhD work, should appear in ToPNoC VI (LNCS 7400).  The web-based
      interface and the aforementioned ltl2tgta tool can be used
      to build testing automata.

    - TGBA can now be reduced by Reverse Simulation (in addition to
      the Direct Simulation introduced in 0.9).  A function called
      iterated_simulations() will alternate direct and reverse
      simulations in a loop as long as it diminishes the size of the
      automaton.

    - The enumerate_cycles class implements the Loizou-Thanisch
      algorithm to enumerate elementary cycles in a SCC.  As an
      example of use, is_weak_scc() will tell whether an SCC is
      inherently weak (all its cycles are accepting, or none of them
      are).

    - parse_lbt() will parse an LTL formula expressed in the prefix
      syntax used (at least) by LBT, LBTT and Scheck.
      to_lbt_string() can be used to print an LTL formula using this
      syntax.

    - to_wring_string() can be used to print an LTL formula into
      Wring's syntax.

    - The LTL/PSL parser now has a lenient mode that can be useful
      to interpret atomic proposition with language-specific constructs.
      In lenient mode, any (...) or {...} block that cannot be parsed
      as formula will be assumed to be an atomic proposition.
      For instance the input (a < b) U (process[2]@ok), normally
      flagged as a syntax error, is read as "a < b" U "process[2]@ok"
      in lenient mode.

    - minimize_obligation() has a new option to disable WDBA
      minimization it cases it would produce a deterministic automaton
      that is bigger than the original TGBA.  This can help
      choosing between less states or more determinism.

    - new functions is_deterministic() and count_nondet_states()
      (The count of nondeterministic states is now displayed on
      automata generated with the web interface.)

    - A new class, "postprocessor", makes it easier to apply
      all available simplification algorithms on a TGBA/BA/Monitors.

  * Minor changes:

    - The '*' operator can (again) be used as an AND in LTL formulas.
      This is for compatibility with formula written in Wring's
      syntax.  However inside SERE it is interpreted as the Kleen
      star.

    - When printing a formula using Spin's LTL syntax, we don't
      double-quote complex atomic propositions (that was not valid
      Spin input anyway).   For instance F"foo == 2" used to be
      output as <>"foo == 2".  We now output <>(foo == 2) instead.
      The latter syntax is understood by Spin 6.  It can be read
      back by Spot in lenient mode (see above).

    - The gspn-ssp benchmark has been removed.


New in spot 0.9.2 (2012-07-02):

  * New features to the web interface.
    - It can run ltl3ba (Babiak et al., TACAS'12) where available.
    - "a loading logo" is displayed when result is not instantaneous.
  * Speed improvements:
    - The unicity hash table of BuDDy has been separated separated
      node table for better cache-friendliness.  The resulting speedup
      is around 5% on BDD-intensive algorithms.
    - A new BDD operation, called bdd_implies() has been added to
      BuDDy to check whether one BDD implies another.  This benefits
      mostly the simulation and degeneralization algorithms of Spot.
    - A new offline implementation of the degeneralization (which
      had always been performed on-the-fly so far) available.  This
      especially helps the Safra complementation.
  * Bug fixes:
    - The CGI script running for ltl2tgba.html will correctly timeout
      after 30s when Spot's translation takes more time.
    - Applying WDBA-minimization on an automaton generated by the
      Couvreur/LaCIM translator could lead to an incorrect automaton
      due to a bug in the definition of product with symbolic
      automata.
    - The Makefile.am of BuDDy, LBTT, and Spot have been adjusted to
      accomodate Automake 1.12 (while still working with 1.11).
    - Better error recovery when parsing broken LTL formulae.
    - Fix errors and warnings reported by clang 3.1 and the
      upcoming g++ 4.8.

New in spot 0.9.1 (2012-05-23):

  * The version of LBTT we distribute includes a patch from Tomáš
    Babiak to count the number of non-deterministic states, and the
    number of deterministic automata produced.
    See lbtt/NEWS for the list of other differences with the original
    version of LBTT 1.2.1.
  * The Couvreur/FM translator has learned two new tricks.  These only
    help to speedup the translation by not issuing states or
    acceptance conditions that would be latter suppresed by other
    optimizations.
    - The translation rules used to translate subformulae of the G
      operator have been adjusted not to produce useless loops
      already implied by G.  This generalizes the "GF" trick
      presented in Couvreur's original FM'99 paper.
    - Promises generated for formula of the form P(a U (b U c))
      are reduced into P(c), avoiding the introduction of many
      promises that imply each other.
  * The tgba_parse() function is now available via the Python
    bindings.
  * Bug fixes:
    - The random SERE generator was using the wrong operators
      for "and" and "or", mistaking And/Or with AndRat/OrRat.
    - The translation of !{r} was incorrect when this subformula
      was recurring (e.g. in G!{r}) and r had loops.
    - Correctly recognize ltl2tgba's option -rL.
    - Using LTL simplification rules based on syntactic implication,
      or based on language containment checks, caused BDD variables
      to be allocated in an "unnatural" order, resulting in a slower
      translation and a less optimal degeneralization.
    - When ltl2tgba reads a neverclaim, it now considers the resulting
      TGBA as a Büchi automaton, and will display double circles in
      the dotty output.

New in spot 0.9 (2012-05-09):

  * New features:
    - Operators from the linear fragment of PSL are supported.  This
      basically extends LTL with Sequential Extended Regulat
      Expressions (SERE), and a couple of operators to bridge SERE and
      LTL.  See doc/tl/tl.pdf for the list of operators and their
      semantics.
    - Formula rewritings have been completely revamped, and augmented
      with rules for PSL operators (and some new LTL rules as well).
      See doc/tl/tl.pdf for the list of the rewritings implemented.
    - Some of these rewritings that may produce larger formulas
      (for instance to rewrite "{a;b;c}" into "a & X(b & Xc)")
      may be explicitely disabled with a new option.
    - The src/ltltest/randltl tool can now generate random SEREs
      and random PSL formulae.
    - Only one translator (ltl2tgba_fm) has been augmented to
      translate the new SERE and PSL operators.  The internal
      translation from SERE to DFA is likely to be rewriten in a
      future version.
    - A new function, length_boolone(), computes the size of an
      LTL/PSL formula while considering that any Boolean term has
      length 1.
    - The LTL/PSL parser recognizes some UTF-8 characters (like ◇ or
      ∧) as operators, and some output routines now have an UTF-8
      output mode.  Tools like randltl and ltl2tgba have gained an -8
      option to enable such output.  See doc/tl/tl.pdf for the list
      of recognized codepoints.
    - A new direct simulation reduction has been implemented.  It
      works directly on TGBAs.  It is in src/tgbaalgos/simlation.hh,
      and it can be tested via ltl2tgba's -RDS option.
    - unabbreviate_wm() is a function that rewrites the W and M operators
      of LTL formulae using R and U.  This is called whenever we output
      a formula in Spin syntax.  By combining this with the aforementioned
      PSL rewriting rules, many PSL formulae that use simple SERE can be
      converted into LTL formulae that can be feed to tools that only
      understand U and R.  The web interface will let you do this.
    - changes to the on-line translator:
      + SVG output is available
      + can display some properties of a formula
      + new options for direct simulation, larger rewritings, and
        utf-8 output
    - configure --without-included-lbtt will prevent LBTT from being
      configured and built.  This helps on systems (such as MinGW)
      where LBTT cannot be built.  The test-suite will skip any
      LBTT-based test if LBTT is missing.
  * Interface changes:
    - Operators ->, <->, U, W, R, and M are now parsed as
      right-associative to better match the PSL standard.
    - The constructors for temporal formulae will perform some trivial
      simplifications based on associativity, commutativity,
      idempotence, and neutral elements.  See doc/tl/tl.pdf for the
      list of such simplifications.
    - Formula instances now have many methods to inspect their
      properties (membership to syntactic classes, absence of X
      operator, etc...) in constant time.
    - LTL/PSL formulae are now handled everywhere as 'const formula*'
      and not just 'formula*'.  This reflects the true nature of these
      (immutable) formula objects, and cleanups a lot of code.
      Unfortunately, it is a backward incompatible change: you may have
      to add 'const' to a couple of lines in your code, and change
      'ltl::const_vistitor' into 'ltl::visitor' if you have written a
      custom visitor.
    - The new entry point for LTL/PSL simplifications is the function
      ltl_simplifier::simplify() declared in src/ltlvisit/simplify.hh.
      The ltl_simplifier class implements a cache.
      Functions such as reduce() or reduce_tau03() are deprecated.
    - The old game-theory-based implementations for direct and delayed
      simulation reductions have been removed.  The old direct
      simulation would only work on degeneralized automata, and yet
      produce results inferior to the new direct simulation introduced
      in this release.  The implementation of delayed simulation was
      unreliable.  The function reduc_tgba_sim() has been kept
      for compatibility (it calls the new direct simulation whatever
      the type of simulation requested) and marked as deprecated.
      ltl2tgba's options -Rd, -RD are gone.  Options -R1t, -R1s,
      -R2s, and -R2t are deprecated and all made equivalent to -RDS.
    - The tgba_explicit hierarchy has been reorganized in order to
      make room for sba_explicit classes that share most of the code.
      The main consequence is that the tgba_explicit type no longuer
      exists.  However the tgba_explicit_number,
      tgba_explicit_formula, and tgba_explicit_string still do.

New in spot 0.8.3 (2012-03-09):

  * Support for both Python 2.x and Python 3.x.
    (Previous versions would only work with Python 2.x.)
  * The online ltl2tgba.html now stores its state in the URL so that
    history is preserved, and links to particular setups can be sent.
  * Bug fixes:
    - Fix a segfault in the compression code used by the -Z
      option of dve2check.
    - Fix a race condition in the CGI script.
    - Fix a segfault in the CGI script when computing a Büchi run.

New in spot 0.8.2 (2012-01-19):

  * configure now has a --disable-python option to disable
    the compilation of Python bindings.
  * Minor speedups in the Safra complementation.
  * Better memory management for the on-the-fly degeneralization
    algorithm.  This mostly benefits to the Safra complementation.
  * Bug fixes:
    - spot::ltl::length() forgot to count the '&' and '|' operators
      in an LTL formula.
    - minimize_wdba() could fail to mark some transiant SCCs as accepting,
      producing an automaton that was not fully minimized.
    - minimize_dfa() could produce incorrect automata, but it is not
      clear whether this could have had an inpact on WDBA minimization
      (the worse case is that some TGBA would not have been minimized
      when they could).
    - Fix a Python syntax error in the CGI script.
    - Fix compilation with g++ 4.0.
    - Fix a make check failure when valgrind is missing.

New in spot 0.8.1 (2011-12-18):

  * Only bug fixes:
    - When ltl2tgba is set to perform both WDBA minimization and
      degeneralization, do the latter only if the former failed.
      In previous version, automata were (uselessly) degeneralized
      before WDBA minimization, causing important slowdowns.
    - Fix compilation with Clang 3.0.
    - Fix a Makefile setup causing a "make check" failure on MacOS X.
    - Fix an mkdir error in the CGI script.

New in spot 0.8 (2011-11-28):

  * Major new features:
    - Spot can read DiVinE models.  See iface/dve2/README for details.
    - The genltl tool can now output 20 different LTL formula families.
      It also replaces the LTLcounter Perl scripts.
    - There is a printer and parser for Kripke structures in text format.
  * Major interface changes:
    - The destructor of all states is now private.  Any code that looks like
      "delete some_state;" will cause an compile error and should be
      updated to "some_state->destroy();".  This new syntax is supported
      since version 0.7.
    - The experimental Nips interface has been removed.
  * Minor changes:
    - The dotty_reachable() function has a new option "assume_sba" that
      can be used for rendering automata with state-based acceptance.
      In that case, acceptance states are displayed with a double
      circle. ltl2tgba (both command line and on-line) Use it to display
      degeneralized automata.
    - The dotty_reachable() function will also display transition
      annotations (as returned by the tgba::transitition_annotation()).
      This can be useful when displaying (small) state spaces.
    - Identifiers used to name atomic proposition can contain dots.
      E.g.: X.Y is now an atomic proposition, while it was understood
      as X&Y in previous versions.
    - The Doxygen documentation is no longer built as a PDF file.
  * Internal improvements:
    - The on-line ltl2tgba CGI script uses a cache to produce faster
      answers.
    - Better memory management for the states of explicit automata.
      Thanks to the aforementioned ->destroy() change, we can avoid
      cloning explicit states.
    - tgba_product has learned how to be faster when one of the operands
      is a Kripke structure (15% speedup).
    - The reduction rule for "a M b" has been improved: it can be
      reduced to "a & b" if "a" is a pure eventuallity.
    - More useless acceptance conditions are removed by SCC simplifications.
  * Bug fixes:
    - Safra complementation has been fixed in cases where more than
      one acceptance conditions where needed to convert the
      deterministic Streett automaton as a TGBA.
    - The degeneralization is now idempotent.  Previously, degeneralizing
      an already degeneralized automaton could add some states.
    - The degeneralization now has a deterministic behavior.  Previously
      it was possible to obtain different output depending on the
      memory layout.
    - Spot now outputs neverclaims with fully parenthesized guards.
      I.e., instead of
         (!x && y) -> goto S1
      it now outputs
         ((!(x)) && (y)) -> goto S1
      This prevents problems when the model defines `x' as
         #define x flag==0
      because !x then evaluated to (!flag)==0 instead of !(flag==0).

New in spot 0.7.1 (2011-02-07):

  * The LTL parser will accept operator ~ (for not) as well
    as --> and <--> (for implication and equivalence), allowing
    formulae from the Büchi Store to be read directly.
  * The neverclaim parser will accept guards of the form
        :: !(...) -> goto ...
    instead of the more commonly used
        :: (!(...)) -> goto ...
    This makes it possible to read neverclaims provided by the Büchi Store.
  * A new ltl2tgba option, -kt, will count the number of "sub-transitions".
    I.e., a transition labelled by "true" counts for 4 "sub-transitions"
    if the automaton uses 2 atomic propositions.
  * Bugs fixed:
    - Fix segfault during WDBA minimization on automata with useless states.
    - Use the included BuDDy library if the one already installed
      is older than the one distributed with Spot 0.7.
    - Fix two typos in the code of the CGI scripts.

New in spot 0.7 (2011-02-01):

  * Spot is now able to read an automaton expressed as a Spin neverclaim.
  * The "experimental" Kripke structure introduced in Spot 0.5 has
    been rewritten, and is no longer experimental.  We have a
    developement version of checkpn using it, and it should be
    released shortly after Spot 0.7.
  * The function to_spin_string(), that outputs an LTL formula using
    Spin's syntax, now takes an optional argument to request
    parentheses at all levels.
  * src/ltltest/genltl is a new tool that generates some interesting
    families of LTL formulae, for testing purpose.
  * bench/ltlclasses/ uses the above tool to conduct the same benchmark
    as in the DepCoS'09 paper by Cichoń et al.  The resulting benchmark
    completes in 12min, while it tooks days (or exhausted the memory)
    when the paper was written (they used Spot 0.4).
  * Degeneralization has again been improved in two ways:
    - It will merge degeneralized transitions that can be merged.
    - It uses a cache to speed up the improvement introduced in 0.6.
  * An implementation of Dax et al.'s paper for minimizing obligation
    formulae has been integrated.  Use ltl2tgba -Rm to enable this
    optimization from the command-line; it will have no effect if the
    property is not an obligation.
  * bench/wdba/ conducts a benchmark similar to the one on Dax's
    webpage, comparing the size of the automata expressing obligation
    formula before and after minimization.  See bench/wdba/README for
    results.
  * Using similar code, Spot can now construct deterministic monitors.
  * New ltl2tgba options:
    -XN: read an input automaton as a neverclaim.
    -C, -CR: Compute (and display) a counterexample after running the
             emptiness check.  With -CR, the counterexample will be
             replayed on the automaton to ensure it is correct
	     (previous version would always compute a replay a
	     counterexample when emptiness-check was enabled)
    -ks: traverse the automaton to compute its number of states and
         transitions (this is faster than -k which will also count
         SCCs and paths).
    -M: Build a deterministic monitor.
    -O: Tell whether a formula represents a safety, guarantee, or
        obligation property.
    -Rm: Minimize automata representing obligation properties.
  * The on-line tool to translate LTL formulae into automata
    has been rewritten and is now at http://spot.lip6.fr/ltl2tgba.html
    It requires a javascript-enabled browser.
  * Bug fixes:
    - Location of the errors messages in the TGBA parser where inaccurate.
    - Various warning fixes for different versions of GCC and Clang.
    - The neverclaim output with ltl2tgba -N or -NN used to ignore any
      automaton simplification performed after degeneralization.
    - The formula simplification based on universality and eventuality
      had a quadratic run-time.

New in spot 0.6 (2010-04-16):

  * Several optimizations to improve some auxiliary steps
    of the LTL translation (not the core of the translation):
    - Better degeneralization
    - SCC simplifications has been tuned for degeneralization
      (ltl2tgba now has two options -R3 and -R3f: the latter will
      remove every acceptance condition that used to be removed
      in Spot 0.5 while the former will leave useless acceptance conditions
      going to accepting SCC.  Experience shows that -R3 is more
      favorable to degeneralization).
    - ltl2tgba will perform SCC optimizations before degeneralization
      and not the converse
    - We added a syntactic simplification rule to rewrite F(a)|F(b) as F(a|b).
      We only had a rule for the more specific FG(a)|FG(b) = F(Ga|Gb).
    - The syntactic simplification rule for F(a&GF(b)) = F(a)&GF(b) has
      be disabled because the latter formula is in fact harder to translate
      efficiently.
  * New LTL operators: W (weak until) and its dual M (strong release)
    - Weak until allows many LTL specification to be specified more
      compactly.
    - All LTL translation algorithms have been updated to
      support these operators.
    - Although they do not add any expressive power, translating
      "a W b" is more efficient (read smaller output automaton) than
      translating the equivalent form using the U operator.
    - Basic syntactic rewriting rules will automatically rewrite "a U
      (b | G(a))" and "(a U b)|G(a)" as "a W b", so you will benefit
      from the new operators even if you do not use them.  Similar
      rewriting rules exist for R and M, although they are less used.
  * New options have been added to the CGI script for
    - SVG output
    - SCC simplifications
  * Bug fixes:
    - The precedence of the "->" and "<->" Boolean operators has been
      adjusted to better match other tools.
      Spot <= 0.5 used to parse "a & b -> c & d" as "a & (b -> c) & d";
      Spot >= 0.6 will parse it as "(a & b) -> (c & d)".