NEWS

New in spot 1.0a (not released):

  * 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.
  * 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)
  * 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 is 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)".
    - The random graph generator was fixed (again!) not to produce
      dead states as documented.
    - Locations in the error messages of the LTL parser were off by one.

New in spot 0.5 (2010-02-01):

  * We have setup two mailing lists:
    - <spot-announce@lrde.epita.fr> is read-only and will be used to
      announce new releases.  You may subscribe at
      https://www.lrde.epita.fr/mailman/listinfo/spot-announce
    - <spot@lrde.epita.fr> can be used to discuss anything related
      to Spot.  You may subscribe at
      https://www.lrde.epita.fr/mailman/listinfo/spot-announce
  * Two new LTL translations have been implemented:
    - eltl_to_tgba_lacim() is a symbolic translation for ELTL based on
      Couvreur's LaCIM'00 paper.  For this translation (available with
      ltl2tgba's option -le), all operators are described as finite
      automata.  A default set of operators is provided for LTL
      (option -lo) and user may add more automaton operators.
    - ltl_to_taa() is a translation based on Tauriainen's PhD thesis.
      LTL is translated to "self-loop" alternating automata
      and then to Transition-based Generalized Automata.  (ltl2tgba's
      option -taa).
    The "Couvreur/FM" translation remains the best LTL translation
    available in Spot.
  * The data structures used to represent LTL formulae have been
    overhauled, and it resulted in a big performence improvement
    (in time and memory consumption) for the LTL translation.
  * Two complementation algorithms for state-based Büchi automata
    have been implemented:
    - tgba_kv_complement is an on-the-fly implementation of the
      Kupferman-Vardi construction (TCS'05) for generalized acceptance
      conditions.
    - tgba_safra_complement is an implementation of Safra's
      complementation.  This algorithm takes a degeneralized Büchi
      automaton as input, but our implementation for the Streett->Büchi
      step will produce a generalized automaton in the end.
  * ltl2tgba has gained several options and the help text has been
    reorganized.  Please run src/tgbatest/ltl2tgba without arguments
    for details.  Couvreur/FM is now the default translation.
  * The ltl2tgba.py CGI script can now run standalone.  It also offers
    the Tauriainen/TAA translation, and some options for SCC-based
    reductions.
  * Automata using BDD-encoded transitions relation can now be pruned
    for useless states symbolically using the delete_unaccepting_scc()
    function.  This is ltl2tgba's -R3b option.
  * The SCC-based simplification (ltl2tgba's -R3 option) has been
    rewritten and improved.
  * The "*" symbol, previously parsed as a synonym for "&" is no
    longer recognized.  This makes room for an upcoming support of
    rational operators.
  * More benchmarks in the bench/ directory:
    - gspn-ssp/    some benchmarks published at ACSD'07,
    - ltlcounter/  translation of a class of LTL formulae used by
                     Rozier & Vardi at SPIN'07
    - scc-stats/   SCC statistics after translation of LTL formulae
    - split-product/ parallelizing gain after splitting LTL automata
  * An experimental Kripke interface has been developed to simplify
    the integration of third party tools that do not use acceptance
    conditions and that have label on states instead of transitions.
    This interface has not been used yet.
  * Experimental interface with the Nips virtual machine.
    It is not very useful as Spot isn't able to retrieve any property
    information from the model.  This will just check assertions.
  * Distribution:
    - The Boost C++ library is now required.
    - Update to Autoconf 2.65, Automake 1.11.1, Libtool 2.2.6b,
      Bison 2.4.1, and Swig 1.3.40.
    - Thanks to the newest Automake, "make check" will now
      run in parallel if you use "make -j2 check" or more.
  * Bug fixes:
    - Disable warnings from the garbage collection of BuDDy, it
      could break the standard output of ltl2tgba.
    - Fix several C++ constructs to ensure Spot will build with
      GCC 4.3, 4.4, and older 3.x releases, as well as with Intel's
      ICC compiler.
    - A very old bug in the hash function for LTL formulae caused Spot
      to sometimes (but very rarely) consider two different LTL formulae
      as equal.

New in spot 0.4 (2007-07-17):

  * Upgrade to Autoconf 2.61, Automake 1.10, Bison 2.3, and Swig 1.3.31.
  * Better LTL simplifications.
  * Don't initialize Buddy if it has already been initialized (in case
    the client software is already using Buddy).
  * Lots of work in the greatspn interface for our ACSD'05 paper.
  * Bug fixes:
    - Fix the random graph generator not to produce dead states as documented.
    - Fix synchronized product in case both side use acceptance conditions.
    - Fix some syntax errors with newer versions of GCC.

New in spot 0.3 (2006-01-25):

  * lbtt 1.2.0
  * The CGI script for LTL translation also offers emptiness check algorithms.
  * tau03_opt_search implements the "ordering heuristic".
    (Submitted by Heikki Tauriainen.)
  * A couple of bugs were fixed into the LTL or automata simplifications.

New in spot 0.2 (2005-04-08):

  * Emptiness checks:
    - the new spot::option_map class is used to pass options to
      emptiness-check algorithms.
    - the new emptiness_check_instantiator class is used to turn a
      string such as `algorithm(option1, option2)' into an actual
      instance of this emptiness-check algorithm with the given
      options.  All tools use this.
    - tau03_opt_search implements the "condition heuristic".
      (Suggested by Heikki Tauriainen.)
  * Minor bug fixes.

New in spot 0.1 (2005-01-31):

  * Emptiness checks:
    - They all follow the same interface, and gather statistical data.
    - New algorithms: gv04.hh, se05.hh, tau03.hh, tau03opt.hh
    - New options for couvreur99: poprem and group.
    - reduce_run() try to reduce accepting runs produced by emptiness checks.
    - replay_run() ensure accepting runs are actually accepting runs.
  * New testing tools:
    - ltltest/randltl: Generate random LTL formulae.
    - tgbatest/randtgba: Generate random TGBAs.  Optionally multiply them
        against random LTL formulae.  Optionally check them for emptiness
        with all available algorithms.  Optionally gather statistics.
  * bench/emptchk/: Contains scripts that benchmark emptiness-checks.
  * Split the degeneralization proxy in two:
    - tgba_tba_proxy  uses at most max(N,1) copies
    - tgba_sba_proxy  uses at most 1+max(N,1) copies and has a
                      state_is_accepting() method
  * tgba::transition_annotation annotate a transition with some string.
    This comes handy to associate that transition to its high-level name.
  * Preliminary support for Event-based GBA (the evtgba*/ directories).
    This might as well disappear in a future release.
  * LTL formulae are now sorting using their string representation, instead
    of their memory address (which is still unique).  This makes the output
    of the various functions more deterministic.
  * The Doxygen documentation is now organized using modules.

New in spot 0.0x (2004-08-13):

  * New atomic_prop_collect() function: collect atomic propositions
    in an LTL formula.
  * Fix several typos in documentation, and some warnings in the code.
  * Now compiles on Darwin and Cygwin.
  * Upgrade to Automake 1.9.1, and lbtt 1.1.2.
    (And drop support for older lbtt versions.)
  * Support newer versions of Valgrind (>= 2.1.0).

New in spot 0.0v (2004-06-29):

  * LTL formula simplifications using basic rewriting rules,
    a-la Wring syntactic approximations, and Etessami's universal
    and existential classes.
     - Function reduce() in ltlvisit/reduce.hh is the main interface.
     - Can be tested with the CGI script.
  * TGBA simplifications using direct simulation, delayed simulation,
    and SCC-based simplifications.  This is still experimental.
  * The LTL parser will now read LTL formulae written using Wring's syntax.
  * ltl2tgba_fm() now has options for on-the-fly fair-loop approximations,
    and Modella-like branching-postponement.
  * GreatSPN interface:
     - The `declarative_environment' is now part of Spot itself rather than
       part of the interface with GreatSPN.
     - the RG and SRG interface can deal with dead markings in three
       ways (omit deadlocks from the state graph, stutter on the deadlock
       and consider as a regular behavior, or stutter and distinguish the
       deadlock with a property).
     - update SSP interface to Soheib Baarir latest work.
  * Preliminary Python bindings for BuDDy's FDD and BVEC.
  * Upgrade to BuDDy 2.3.

New in spot 0.0t (2004-04-23):

  * `emptiness_check':
      - fix two bugs in the computation of the counter example,
      - revamp the interface for better customization.
  * `never_claim_reachable': new function.
  * Introduce annonymous BDD variables in `bdd_dict', and start
    to use it in `ltl_to_tgba_fm'.
  * Offer never claim in the CGI script.
  * Rename EESRG as SSP, and offer specialized variants of the
    emptiness_check.

New in spot 0.0r (2004-03-08):

  * In ltl_to_tgba_fm:
    - New option `exprop' to optimize determinism.
    - Make the `symbolic indentification' from 0.0p optional.
  * `nonacceptant_lbtt_reachable' new function to help getting
    accurate statistics from LBTT.
  * Revamp the cgi script's user interface.
  * Upgrade to lbtt 1.0.3, swig 1.3.21, automake 1.8.3

New in spot 0.0p (2004-02-03):

  * In ltl_to_tgba_fm:
    - identify states with identical symbolic expansions
      (i.e., identical continuations)
    - use Acc[b] as acceptance condition for Fb, not Acc[Fb].
  * Update and speed-up the cgi script.
  * Improve degeneralization.

New in spot 0.0n (2004-01-13):

  * emptiness_check::check2() is a variant of Couvreur's emptiness check that
    explores visited states first.
  * Build the EESRG supporting code condinally, as the associated
    GreatSPN changes have not yet been contributed to GreatSPN.
  * Add a powerset algorithm (determinize TGBA ignoring acceptance
    conditions, i.e., as if they were used to recognize finite languages).
  * tgba_explicit::merge_transitions: merge transitions with same source,
    destination, and acceptance condition.
  * Run test cases within valgrind.
  * Various bug fixes.

New in spot 0.0l (2003-12-01):

  * Computation of prime implicants.  This simplify the output of
    ltl_to_tgba_fm, and allows conditions to be output as some of
    product in dot output.
  * Optimize translation of GFy in ltl_to_tgba_fm.
  * tgba_explicit supports arbitrary binary formulae on transitions
    (only conjunctions were allowed).

New in spot 0.0j (2003-11-03):

  * Use hash_map's instead of map's almost everywhere.
  * New emptiness check, based on Couvreur's algorithm.
  * LTL propositions can be put inside doublequotes to disambiguate
    some constructions.
  * Preliminary support for GreatSPN's EESRG.
  * Various bug fixes.

New in spot 0.0h (2003-08-18):

  * More python bindings:
    - "import buddy" works (see wrap/python/tests/bddnqueen.py for an example),
    - almost all the Spot API is now available via "import spot".
  * wrap/python/cgi/ltl2tgba.py is an LTL-to-Büchi translator that
    work as as a cgi script.
  * Couvreur's FM'99 ltl-to-tgba translation.

New in spot 0.0f (2003-08-01):

  * More python bindings, still only for the spot::ltl:: namespace.
  * Functional GSPN interface.  (Enable with --with-gspn=directory.)
  * The LTL scanner recognizes /\, \/, and xor.
  * Upgrade to lbtt 1.0.2.
  * tgba_tba_proxy is an on-the-fly degeneralizer.
  * Implements the "magic search" algorithm.
    (Works only on a tgba_tba_proxy.)
  * Tgba's output algorithms (save(), dotty()) now non-recursive.
  * During products, succ_iter will optimize its set of successors
    using information computed from the current product state.
  * BDD dictionnaries are now shared between automata and.  This
    gets rid of all the BDD-variable translating machinery.

New in spot 0.0d (2003-07-13):

  * Optimize translation of G operators occurring at the root
    of a formula (or its immediate children when the root is a
    conjunction).  This saves two BDD variables per G operator.
  * Distribute lbtt, and run it during `make check'.
  * First sketch of GSPN interface.
  * succ_iter_concreate::next() completely rewritten.
  * Transitions are now labelled by boolean formulae (not only
    conjunctions).
  * Documentation:
    - Output collaboration diagrams.
    - Build and distribute PDF manual.
  * Many bug fixes.

New in spot 0.0b (2003-06-26):

  * Everything.