NEWS

New in spot 2.3.5.dev (not yet released)

  Tools:

  - genaut is a new binary that produces families of automata defined
    in the literature (in the same way as we have genltl for LTL
    formulas).

  - autcross is a new binary that compares the output of tools
    transforming automata (in the same way as we have ltlcross for
    LTL translators).

  - autfilt learned to build the union (--sum) or the intersection
    (--sum-and) of two language by putting two automata side-by-side
    and fiddling with the initial states.  This complement the already
    implemented intersection (--product) and union (--product-or),
    both based on a product.

  - autfilt learned to complement any alternating automaton with
    option --dualize.

  - autfilt learned --split-edges to convert labels that are Boolean
    formulas into labels that are min-terms.  (See spot::split_edges()
    below.)

  - autfilt learned --simplify-acceptance to simplify some acceptance
    conditions.  (See spot::simplify_acceptance() below.)

  - autfilt --decompote-strength has been renamed to --decompose-scc
    because it can now extract the subautomaton leading to an SCC
    specified by number.  (The old name is still kept as an alias.)

  Library:

  - A new library, libspotgen, gathers all functions used to generate
    families of automata or LTL formulas, used by genltl and genaut.

  - spot::sum() and spot::sum_and() implements the union and the
    intersection of two automatons by putting them side-by-side and
    using non-deterministim or universal branching on the initial
    statae.

  - twa objects have a new property: prop_complete().  This obviously
    acts as a cache for the is_complete() function.

  - spot::dualize() completements any alternating automaton.  Since
    the dual of a deterministic automaton is still deterministic, the
    function spot::dtwa_complement() has been deprecated and simply
    calls spot::dualize().

  - spot::dtwa_complement now simply returns the result of dualize()

  - spot::decompose_strength() was extended and renamed to
    spot::decompose_scc() as it can now also extract a subautomaton
    leading to a particular SCC.  A demonstration of this feature via
    the Python bindings can be found at
    https://spot.lrde.epita.fr/ipynb/decompose.html

  - A new named property for automata called "original-states" can be
    used to record the origin of a state before transformation.  It is
    currently defined by the degeneralization algorithms, and by
    transform_accessible() and algorithms based on it (like
    remove_ap::strip(), decompose_strength(), decompose_scc()).  This
    is realy meant as an aid for writing algorithms that need this
    mapping, but it can also be used to debug these algorithms: the
    "original-states" information is displayed by the dot printer when
    the 'd' option is passed.  For instance in

      % ltl2tgba 'GF(a <-> Fb)' --dot=s
      % ltl2tgba 'GF(a <-> Fb)' | autfilt -B --dot=ds

    the second command outputs an automaton with states that show
    references to the first one.

  - A new named property for automata called "degen-levels" keeps track
    of the level of a state in a degeneralization. This information
    complements the one carried in "original-states".

  - A new named property for automata called "simulated-states" can be
    used to record the origin of a state through simulation. The
    behavior is similar to "original-states" above. Determinization
    takes advantage of this in its pretty print.

  - The new function spot::acc_cond::is_streett_like() checks whether
    an acceptance condition is conjunction of disjunctive clauses
    containing at most one Inf and at most one Fin.  It builds a
    vector of pairs to use if we want to assume the automaton has
    Streett acceptance.  The dual function is
    spot::acc_cond::is_rabin_like() works similarly.

  - The degeneralize() function has learned to consider acceptance
    marks common to all edges comming to a state to select its initial
    level.  A similar trick was already used in sbacc(), and saves a
    few states in some cases.

  - There is a new spot::split_edges() function that transforms edges
    (labeled by Boolean formulas over atomic propositions) into
    transitions (labeled by conjunctions where each atomic proposition
    appear either positive or negative).  This can be used to
    preprocess automata before feeding them to algorithms or tools
    that expect transitions labeled by letters.

  - spot::scc_info has two new methods to easily iterate over the
    edges of an SCC: edges_of() and inner_edges_of().

  - spot::scc_info can now be passed a filter function to ignore
    or cut some edges.

  - spot::scc_info now keeps track of acceptance sets that are common
    to all edges in an SCC.  These can be retrieved using
    scc_info::common_sets_of(scc), and they are used by scc_info to
    classify some SCCs as rejecting more easily.

  - The new function acc_code::remove() removes all the given
    acceptance sets from the acceptance condition.

  - It is now possible to change an automaton acceptance condition
    directly by calling twa::set_acceptance().

  - spot::cleanup_acceptance_here now takes an additional boolean
    parameter specifying whether to strip useless marks from the
    automaton.  This parameter is defaulted to true, in order to
    keep this modification backward-compatible.

  - The new function spot::simplify_acceptance() is able to perform
    some simplifications on an acceptance condition, and might lead
    to the removal of some acceptance sets.

  - The function spot::streett_to_generalized_buchi() is now able to
    work on automatons with Streett-like acceptance.

  - spot::relabel_here() was used on automata to rename atomic
    propositions, it can now replace atomic propositions by Boolean
    subformula.  This makes it possible to use relabeling maps
    produced by relabel_bse() on formulas.

  - twa_graph::copy_state_names_from() can be used to copy the state
    names from another automaton, honoring "original-states" if
    present.

  - Building automata for LTL formula with a large number N of atomic
    propositions can be costly, because several loops and
    data-structures are exponential into N.  However a formula like
      ((a & b & c) | (d & e & f)) U ((d & e & f) | (g & h & i))
    can be translated more efficiently by first building an automaton
    for (p0 | p1) U (p1 | p2), and then substituting p0, p1, p2 by the
    appropriate Boolean formula.  Such a trick is now attempted
    for translation of formulas with 4 atomic propositions or
    more (this threshold can be changed, see -x relabel-bool=N in
    the spot-x(7) man page).

  - The new function spot::to_weak_alternating() is able to take an
    input automaton with generalized Büchi/co-Büchi acceptance and
    convert it to a weak alternating automaton.

  - spot::sbacc() is now able to work on alternating automata.

  - spot::sbacc() and spot::degeneralize() learned to merge
    accepting sinks.

  - If the SPOT_BDD_TRACE envorinment variable is set, statistics
    about BDD garbage collection and table resizing are shown.

  - The & and | operators for acceptannce conditions have been changed
    slightly to be more symmetrical.  In older version, operator &
    would move Fin() terms to the front, but that is not the case
    anymore.  Also operator & was already grouping all Inf() terms
    (for efficiency reasons), in this version operator | is
    symmetrically grouping all Fin() terms.

  - The automaton parser is now reentrant, making it possible to
    process automata from different streams at the same time (i.e.,
    using multiple spot::automaton_stream_parser instances at once).

  - The print_hoa() and parse_automaton() functions have been updated
    to recognize the "exist-branch" property of the non-released HOA
    v1.1, as well as the new meaning of property "deterministic".  (In
    HOA v1 "properties: deterministic" means that the automaton has no
    existential branching; in HOA v1.1 it disallows universal
    branching as well.)  The meaning of "deterministic" in Spot has
    been adjusted to these new semantics, see "Backward-incompatible
    changes" below.

  - The parser for HOA now recognize and verifies correct use of the
    "univ-branch" property.  This is known to be a problem with option
    -H1 of ltl3ba 1.1.2 and ltl3dra 0.2.3, so the environment variable
    SPOT_HOA_TOLERANT can be set to disable the diagnostic.

  Python:

  - The 'spot.gen' package exports the functions from libspotgen.
    See https://spot.lrde.epita.fr/ipynb/gen.html for examples.

  Backward-incompatible changes:

  - spot::acc_cond::mark_t::operator bool() has been marked as
    explicit.  The implicit converion to bool (and, via bool, to int)
    was a source of bugs.

  - spot::twa_graph::set_init_state(const state*) has been removed.
    It was never used.  You always want to use
    spot::twa_graph::set_init_state(unsigned) in practice.

  - The previous implementation of spot::is_deterministic() has been
    renamed to spot::is_universal().  The new version of
    spot::is_deterministic() requires the automaton to be both
    universal and existential.  This should not make any difference in
    existing code unless you work with the recently added support for
    alternating automata.

  - spot::acc_cond::mark_t::sets() now returns an internal iterable
    object instead of an std::vector<unsigned>.

  Deprecation notice:

  - spot::decompose_strength() is deprecated, it has been renamed
    to spot::decompose_scc().

  - spot::dtwa_complement() is deprecated.  Prefer the more generic
    spot::dualize() instead.

  - The spot::twa::prop_deterministic() methods have been renamed to
    spot::twa::prop_universal() for consistency with the change to
    is_deterministic() listed above.  We have kept
    spot::twa::prop_deterministic() as a deprecated synonym for
    spot::twa::prop_universal() to help backward compatibility.

  - The spot::copy() function is deprecated.  Use
    spot::make_twa_graph() instead.

New in spot 2.3.5 (2017-06-22)

  Bugs fixed:

  - We have fixed new cases where translating multiple formulas in a
    single ltl2tgba run could produce automata different from those
    produced by individual runs.

  - The print_dot() function had a couple of issues when printing
    alternating automata: in particular, when using flag 's' (display
    SCC) or 'y' (split universal destination by colors) universal
    edges could be connected to undefined states.

  - Using --stats=%s or --stats=%s or --stats=%t could take an
    unnecessary long time on automata with many atomic propositions,
    due to a typo.  Furthermore, %s/%e/%t/%E/%T were printing
    a number of reachable states/edges/transitions, but %S was
    incorrectly counting all states even unreachable.

  - Our verson of BuDDy had an incorrect optimization for the
    biimp operator.

New in spot 2.3.4 (2017-05-11)

  Bugs fixed:

  - The transformation to state-based acceptance (spot::sbacc()) was
    incorrect on automata where the empty acceptance mark is accepting.

  - The --help output of randaut and ltl2tgba was showing an
    unsupported %b stat.

  - ltldo and ltlcross could leave temporary files behind when
    aborting on error.

  - The LTL simplifcation rule that turns F(f)|q into F(f|q)
    when q is a subformula that is both eventual and universal
    was documented but not applied in some forgotten cases.

  - Because of some caching inside of ltl2tgba, translating multiple
    formula in single ltl2tgba run could produce automata different
    from those produced by individual runs.

New in spot 2.3.3 (2017-04-11)

  Tools:

  - ltldo and ltlcross learned shorthands to talk to ltl2da, ltl2dpa,
    and ltl2ldba (from Owl) without needing to specify %f>%O.

  - genltl learned --spec-patterns as an alias for --dac-patterns; it
    also learned two new sets of LTL formulas under --hkrss-patterns
    (a.k.a. --liberouter-patterns) and --p-patterns
    (a.k.a. --beem-patterns).

  Bugs fixed:

  - In "lenient" mode the formula parser would fail to recover from a
    missing closing brace.

  - The output of 'genltl --r-left=1 --r-right=1 --format=%F' had
    typos.

  - 'ltl2tgba Fa | autfilt --complement' would incorrectly claim that
    the output is "terminal" because dtwa_complement() failed to reset
    that property.

  - spot::twa_graph::purge_unreachable_states() was misbehaving on
    alternating automata.

  - In bench/stutter/ the .cc files were not compiling due to warnings
    being caught as errors.

  - The code in charge of detecting DBA-type Rabin automata is
    actually written to handle a slightly larger class of acceptance
    conditions (e.g., Fin(0)|(Fin(1)&Inf(2))), however it failed to
    correctly detect DBA-typeness in some of these non-Rabin
    acceptance.

New in spot 2.3.2 (2017-03-15)

  Tools:

  - In tools that output automata, the number of atomic propositions
    can be output using --stats=%x (output automaton) or --stats=%X
    (input automaton).  Additional options can be passed to list
    atomic propositions instead of counting them.  Tools that output
    formulas also support --format=%x for this purpose.

  Python:

  - The bdd_to_formula(), and to_generalized_buchi() functions can now
    be called in Python.

  Documentation:

  - https://spot.lrde.epita.fr/tut11.html is a new page describing
    how to build monitors in Shell, Python, or C++.

  Bugs fixed:

  - The tests using LTSmin's patched version of divine would fail
    if the current (non-patched) version of divine was installed.

  - Because of a typo, the output of --stats='...%P...' was correct
    only if %p was used as well.

  - genltl was never meant to have (randomly attributed) short
    options for --postive and --negative.

  - a typo in the code for transformating transition-based acceptance
    to state-based acceptance could cause a superfluous initial state
    to be output in some cases (the result was still correct).

  - 'ltl2tgba --any -C -M ...' would not complete automata.

  - While not incorrect, the HOA properties output by 'ltl2tgba -M'
    could be 'inherently-weak' or 'terminal', while 'ltl2tgba -M -D'
    would always report 'weak' automata.  Both variants now report the
    most precise between 'weak' or 'terminal'.

  - spot::twa_graph::set_univ_init_state() could not be called with
    an initializer list.

  - The Python wrappers for spot::twa_graph::state_from_number and
    spot::twa_graph::state_acc_sets were broken in 2.3.

  - Instantiating an emptiness check on an automaton with unsupported
    acceptance condition should throw an exception.  This used to be
    just an assertion, disabled in release builds; the difference
    matters for the Python bindings.

  Deprecation notice:

  - Using --format=%a to print the number of atomic propositions in
    ltlfilt, genltl, and randltl still works, but it is not documented
    anymore and should be replaced by the newly-introduced --format=%x
    for consistency with tools producing automata, where %a means
    something else.


New in spot 2.3.1 (2017-02-20)

  Tools:

  - ltldo learnt to act like a portfolio: --smallest and --greatest
    will select the best output automaton for each formula translated.
    See https://spot.lrde.epita.fr/ltldo.html#portfolio for examples.

  - The colors used in the output of ltlcross have been adjusted to
    work better with white backgrounds and black backgrounds.

  - The option (y) has been added to --dot. It splits the universal
    edges with the same targets but different colors.

  - genltl learnt three new families for formulas: --kr-n2=RANGE,
    --kr-nlogn=RANGE, and --kr-n=RANGE.  These formulas, from
    Kupferman & Rosenberg [MoChArt'10] are recognizable by
    deterministic Büchi automata with at least 2^2^n states.

  Library:

  - spot::twa_run::as_twa() has an option to preserve state names.

  - the method spot::twa::is_alternating(), introduced in Spot 2.3 was
    badly named and has been deprecated.  Use the negation of the new
    spot::twa::is_existential() instead.

  Bugs fixed:

  - spot::otf_product() was incorrectly registering atomic
    propositions.

  - spot::ltsmin_model::kripke() forgot to register the "dead"
    proposition.

  - The spot::acc_word type (used to construct acceptance condition)
    was using some non-standard anonymous struct.  It is unlikely that
    this type was actually used outside Spot, but if you do use it,
    spot::acc_word::op and spot::acc_word::type had to be renamed as
    spot::acc_word::sub.op and spot::acc_word::sub.type.

  - alternation_removal() was not always reporting the unsupported
    non-weak automata.

  - a long-standing typo in the configure code checking for Python
    caused any user-defined CPPFLAGS to be ignored while building
    Spot.

  - The display of clusters with universal edges was confused, because the
    intermediate node was not in the cluster even if one of the target was
    in the same one.

New in spot 2.3 (2017-01-19)

  Build:

  * While Spot only relies on C++11 features, the configure script
    learned --enable-c++14 to compile in C++14 mode.  This allows us
    check that nothing breaks when we will switch to C++14.

  * Spot is now distributed with PicoSAT 965, and uses it for
    SAT-based minimization of automata without relying on temporary
    files.  It is still possible to use an external SAT solver by
    setting the SPOT_SATSOLVER environment variable.

  * The development Debian packages for Spot now install static
    libraries as well.

  * We now install configuration files for users of pkg-config.

  Tools:

  * ltlcross supports translators that output alternating automata in
    the HOA format.  Cross-comparison checks will only work with weak
    alternating automata (not necessarily *very* weak), but "ltlcross
    --no-check --product=0 --csv=..." will work with any alternating
    automaton if you just want satistics.

  * autfilt can read alternating automata.  This is still experimental
    (see below). Some of the algorithms proposed by autfilt will
    refuse to work because they have not yet been updated to work with
    alternating automata, but in any case they should display a
    diagnostic: if you see a crash, please report it.

  * autfilt has three new filters: --is-very-weak, --is-alternating,
    and --is-semi-deterministic.

  * the --check option of autfilt/ltl2tgba/ltldo/dstar2tgba can now
    take "semi-determinism" as argument.

  * autfilt --highlight-languages will color states that recognize
    identical languages.  (Only works for deterministic automata.)

  * 'autfilt --sat-minimize' and 'ltl2tgba -x sat-minimize' have
    undergone some backward incompatible changes.  They use binary
    search by default, and support different options than they used
    too.  See spot-x(7) for details.  The defaults are those that were
    best for the benchmark in bench/dtgbasat/.

  * ltlfilt learned --recurrence and --persistence to match formulas
    belonging to these two classes of the temporal hierarchy.  Unlike
    --syntactic-recurrence and --syntactic-persistence, the new checks
    are automata-based and will also match pathological formulas.
    See https://spot.lrde.epita.fr/hierarchy.html

  * The --format option of ltlfilt/genltl/randltl/ltlgrind learned to
    print the class of a formula in the temporal hierarchy of Manna &
    Pnueli using %h.  See https://spot.lrde.epita.fr/hierarchy.html

  * ltldo and ltlcross learned a --relabel option to force the
    relabeling of atomic propositions to p0, p1, etc.  This is more
    useful with ltldo, as it allows calling a tool that restricts the
    atomic propositions it supports, and the output automaton will
    then be fixed to use the original atomic propositions.

  * ltldo and ltlcross have learned how to call ltl3hoa, so
    'ltl3hoa -f %f>%O' can be abbreviated to just 'ltl3hoa'.

  Library:

  * A twa is required to have at least one state, the initial state.
    An automaton can only be empty while it is being constructed,
    but should not be passed to other algorithms.

  * Couvreur's emptiness check has been rewritten to use the explicit
    interface when possible, to avoid overkill memory allocations.
    The new version has further optimizations for weak and terminal
    automata.  Overall, this new version is roughly 4x faster on
    explicit automata than the former one.  The old version has been
    kept for backward compatibility, but will be removed eventually.

  * The new version of the Couvreur emptiness check is now the default
    one, used by twa::is_empty() and twa::accepting_run().  Always
    prefer these functions over an explicit call to Couvreur.

  * experimental support for alternating automata:

    - twa_graph objects can now represent alternating automata.  Use
      twa_graph::new_univ_edge() and twa_graph::set_univ_init_state()
      to create universal edges an initial states; and use
      twa_graph::univ_dests() to iterate over the universal
      destinations of an edge.

    - the automaton parser will now read alternating automata in the
      HOA format.  The HOA and dot printers can output them.

    - the file twaalgos/alternation.hh contains a few algorithms
      specific to alternating automata:
      + remove_alternation() will transform *weak* alternating automata
        into TGBA.
      + the class outedge_combiner can be used to perform "and" and "or"
        on the outgoing edges of some alternating automaton.

    - scc_info has been adjusted to handle universal edges as if they
      were existential edges.  As a consequence, acceptance
      information is not accurate.

    - postprocessor will call remove_alternation() right away, so
      it can be used as a way to transform alternating automata
      into different sub-types of (generalized) Büchi automata.
      Note that although prostprocessor optimize the resulting
      automata, it still has no simplification algorithms that work
      at the alternating automaton level.

    - See https://spot.lrde.epita.fr/tut23.html
      https://spot.lrde.epita.fr/tut24.html and
      https://spot.lrde.epita.fr/tut31.html for some code examples.

  * twa objects have two new properties, very-weak and
    semi-deterministic, that can be set or retrieved via
    twa::prop_very_weak()/twa::prop_semi_deterministic(), and that can
    be tested by is_very_weak_automaton()/is_semi_deterministic().

  * twa::prop_set has a new attribute used in twa::prop_copy() and
    twa::prop_keep() to indicate that determinism may be improved by
    an algorithm.  In other words properties like
    deterministic/semi-deterministic/unambiguous should be preserved
    only if they are positive.

  * language_map() and highlight_languages() are new functions that
    implement autfilt's --highlight-languages option mentionned above.

  * dtgba_sat_minimize_dichotomy() and dwba_sat_minimize_dichotomy()
    use language_map() to estimate a lower bound for binary search.

  * The encoding part of SAT-based minimization consumes less memory.

  * SAT-based minimization of automata can now be done using two
    incremental techniques that take a solved minimization and attempt
    to forbid the use of some states.  This is done either by adding
    clauses, or by using assumptions.

  * If the environment variable "SPOT_XCNF" is set during incremental
    SAT-based minimization, XCNF files suitable for the incremental SAT
    competition will be generated.  This requires the use of an exteral
    SAT solver, setup with "SPOT_SATSOLVER".  See spot-x(7).

  * The new function mp_class(f) returns the class of the formula
    f in the temporal hierarchy of Manna & Pnueli.

Python:

  * spot.show_mp_hierarchy() can be used to display the membership of
    a formula to the Manna & Pnueli hierarchy, in notebooks.  An
    example is in https://spot.lrde.epita.fr/ipynb/formulas.html

  * The on-line translator will now display the temporal hierarchy
    in the "Formula > property information" output.

Bugs fixed:

  * The minimize_wdba() function was not correctly minimizing automata
    with useless SCCs.  This was not an issue for the LTL translation
    (where useless SCCs are always removed first), but it was an issue
    when deciding if a formula was safety or guarantee.  As a
    consequence, some tricky safety or guarantee properties were only
    recognized as obligations.

  * When ltlcross was running a translator taking the Spin syntax as
    input (%s) it would not automatically relabel any unsupported
    atomic propositions as ltldo already do.

  * When running "autfilt --sat-minimize" on a automaton representing
    an obligation property, the result would always be a complete
    automaton even without the -C option.

  * ltlcross --products=0 --csv should not output any product-related
    column in the CSV output since it has nothing to display there.

New in spot 2.2.2 (2016-12-16)

  Build:

  * If the system has an installed libltdl library, use it instead of
    the one we distribute.

  Bug fixes:

  * scc_filter() had a left-over print statement that would print
    "names" when copying the name of the states.

  * is_terminal() should reject automata that have accepting
    transitions going into rejecting SCCs.  The whole point of
    being a terminal automaton is that reaching an accepting
    transition guarantees that any suffix will be accepted.

  * The HOA parser incorrectly read "Acceptance: 1 Bar(0)" as a valid
    way to specify "Acceptance: 1 Fin(0)" because it assumed that
    everything that was not Inf was Fin.  These errors are now
    diagnosed.

  * Some of the installed headers (spot/misc/fixpool.hh,
    spot/misc/mspool.hh, spot/twaalgos/emptiness_stats.hh) were not
    self-contained.

  * ltlfilt --from-ltlf should ensure that "alive" holds initially in
    order to reject empty traces.

  * the on-line translator had a bug where a long ltl3ba process would
    continue running even after the script had timeout'ed.

New in spot 2.2.1 (2016-11-21)

  Bug fix:

  * The bdd_noderesize() function, as modified in 2.2, would always
    crash.

New in spot 2.2 (2016-11-14)

  Command-line tools:

  * ltlfilt has a new option --from-ltlf to help reducing LTLf (i.e.,
    LTL over finite words) model checking to LTL model checking.  This
    is based on a transformation by De Giacomo & Vardi (IJCAI'13).

  * "ltldo --stats=%R", which used to display the serial number of the
    formula processed, was renamed to "ltldo --stats=%#" to free %R
    for the following feature.

  * autfilt, dstar2tgba, ltl2tgba, ltlcross, ltldo learned to measure
    cpu-time (as opposed to wall-time) using --stats=%R.  User or
    system time, for children or parent, can be measured separately by
    adding additional %[LETTER]R options.  The difference between %r
    (wall-clock time) and %R (CPU time) can also be used to detect
    unreliable measurements.  See
      https://spot.lrde.epita.fr/oaut.html#timing

  Library:

  * from_ltlf() is a new function implementing the --from-ltlf
    transformation described above.

  * is_unambiguous() was rewritten in a more efficient way.

  * scc_info learned to determine the acceptance of simple SCCs made
    of a single self-loop without resorting to remove_fin() for complex
    acceptance conditions.

  * remove_fin() has been improved to better deal with automata with
    "unclean" acceptance, i.e., acceptance sets that are declared but
    not used.  In particular, this helps scc_info to be more efficient
    at deciding the acceptance of SCCs in presence of Fin acceptance.

  * Simulation-based reductions now implement just bisimulation-based
    reductions on deterministic automata, to save time.  As an example,
    this halves the run time of
       genltl --rv-counter=10 | ltl2tgba

  * scc_filter() learned to preserve state names and highlighted states.

  * The BuDDy library has been slightly optimized: the initial setup
    of the unicity table can now be vectorized by GCC, and all calls
    to setjmp are now avoided when variable reordering is disabled
    (the default).

  * The twa class has three new methods:
      aut->intersects(other)
      aut->intersecting_run(other)
      aut->intersecting_word(other)
    currently these are just convenient wrappers around
      !otf_product(aut, other)->is_empty()
      otf_product(aut, other)->accepting_run()->project(aut)
      otf_product(aut, other)->accepting_word()
    with any Fin-acceptance removal performed before the product.
    However the plan is to implement these more efficiently in the
    future.

  Bug fixes:

  * ltl2tgba was always using the highest settings for the LTL
    simplifier, ignoring the --low and --medium options.  Now
      genltl --go-theta=12 | ltl2tgba --low --any
    is instantaneous as it should be.

  * The int-vector compression code could encode 6 and 22 in the
    same way, causing inevitable issues in our LTSmin interface.
    (This affects tests/ltsmin/modelcheck with option -z, not -Z.)

  * str_sere() and str_utf8_sere() were not returning the same
    string that print_sere() and print_utf8_sere() would print.

  * Running the LTL parser in debug mode would crash.

  * tgba_determinize() could produce incorrect deterministic automata
    when run with use_simulation=true (the default) on non-simplified
    automata.

  * When the automaton_stream_parser reads an automaton from an
    already opened file descriptor, it will not close the file
    anymore.  Before that the spot.automata() python function used to
    close a file descriptor twice when reading from a pipe, and this
    led to crashes of the 0MQ library used by Jupyter, killing the
    Python kernel.

  * remove_fin() could produce incorrect result on incomplete
    automata tagged as weak and deterministic.

  * calling set_acceptance() several times on an automaton could
    result in unexpected behaviors, because set_acceptance(0,...)
    used to set the state-based acceptance flag automatically.

  * Some buffering issue caused syntax errors to be displayed out
    of place by the on-line translator.

New in spot 2.1.2 (2016-10-14)

  Command-line tools:

  * genltl learned 5 new families of formulas
    (--tv-f1, --tv-f2, --tv-g1, --tv-g2, --tv-uu)
    defined in Tabakov & Vardi's RV'10 paper.

  * ltlcross's --csv and --json output was changed to not include
    information about the ambiguity or strength of the automata by
    default.   Computing those can be costly and not needed by
    every user, so it should now be requested explicitely using
    options --strength and --ambiguous.

  Library:

  * New LTL simplification rule:

    - GF(f & q) = G(F(f) & q) if q is
      purely universal and a pure eventuality.  In particular
      GF(f & GF(g)) now ultimately simplifies to G(F(f) & F(g)).

  Bug fixes:

  * Fix spurious uninitialized read reported by valgrind when
    is_Kleene_star() is compiled by clang++.

  * Using "ltlfilt some-large-file --some-costly-filter" could take
    to a lot of time before displaying the first results, because the
    output of ltlfilt is buffered: the buffer had to fill up before
    being flushed.  The issue did not manifest when the input is
    standard input, because of the C++ feature that reading std::cin
    should flush std::cout; however it was well visible when reading
    from files.  Flushing is now done more regularly.

  * Fix compilation warnings when -Wimplicit-fallthrough it enabled.

  * Fix python errors on Darwin when using methods from the spot module
    inside of the spot.ltsmin submodule.

  * Fix ltlcross crash when combining --no-check with --verbose.

  * Adjust paths and options used in bench/dtgbasat/ to match the
    changes introduced in Spot 2.0.

New in spot 2.1.1 (2016-09-20)

  Command-line tools:

  * ltlfilt, randltl, genltl, and ltlgrind learned to display the size
    (%s), Boolean size (%b), and number of atomic propositions (%a)
    with the --format and --output options.  A typical use-case is to
    sort formulas by size:
       genltl --dac --format='%s,%f' | sort -n | cut -d, -f2
    or to group formulas by number of atomic propositions:
       genltl --dac --output='ap-%a.ltl'

  * autfilt --stats learned the missing %D, %N, %P, and %W sequences,
    to complete the existing %d, %n, %p, and %w.

  * The --stats %c option of ltl2tgba, autfilt, ltldo, and dstar2tgba
    now accepts options to filter the SCCs to count.  For instance
    --stats='%[awT]c' will count the SCCs that are (a)ccepting and
    (w)eak, but (not t)erminal.  See --help for all supported filters.

  Bugs fixed:

  * Fix several cases where command-line tools would fail to diagnose
    write errors (e.g. when writing to a filesystem that is full).
  * Typos in genltl --help and in the man page spot-x(7).

New in spot 2.1 (2016-08-08)

  Command-line tools:

  * All tools that input formulas or automata (i.e., autfilt,
    dstar2tgba, ltl2tgba, ltl2tgta, ltlcross, ltldo, ltlfilt,
    ltlgrind) now have a more homogeneous handling of the default
    input.

    - If no formula/automaton have been specified, and the standard
    input is a not a tty, then the default is to read that. This is a
    change for ltl2tgba and ltl2tgta.  In particular, it simplifies

        genltl --dac | ltl2tgba -F- | autfilt ...

    into

        genltl --dac | ltl2tgba | autfilt ...

    - If standard input is a tty and no other input has been
    specified, then an error message is printed.  This is a change for
    autfilt, dstar2tgba, ltlcross, ltldo, ltlfilt, ltlgrind, that used
    to expect the user to type formula or automata at the terminal,
    confusing people.

    - All tools now accept - as a shorthand for -F-, to force reading
    input from the standard input (regardless of whether it is a tty
    or not).  This is a change for ltl2tgba, ltl2tgta, ltlcross, and
    ltldo.

  * ltldo has a new option --errors=... to specify how to deal
    with errors from executed tools.

  * ltlcross and ltldo learned to bypass the shell when executing
    simple commands (with support for single or double-quoted
    arguments, and redirection of stdin and stdout, but nothing more).

  * ltlcross and ltldo learned a new syntax to specify that an input
    formula should be written in some given syntax after rewriting
    some operators away.  For instance the defaults arguments passed
    to ltl2dstar have been changed from
         --output-format=hoa %L %O
    into
         --output-format=hoa %[WM]L %O
    where [WM] specifies that operators W and M should be rewritten
    away.  As a consequence running
         ltldo ltl2dstar -f 'a M b'
    will now work and call ltl2dstar on the equivalent formula
    'b U (a & b)' instead.  The operators that can be listed between
    brackets are the same as those of ltlfilt --unabbreviate option.

  * ltlcross learned to show some counterexamples when diagnosing
    failures of cross-comparison checks against random state spaces.

  * autfilt learned to filter automata by count of SCCs (--sccs=RANGE)
    or by type of SCCs (--accepting-sccs=RANGE,
    --rejecting-sccs=RANGE, trivial-sccs=RANGE, --terminal-sccs=RANGE,
    --weak-sccs=RANGE, --inherently-weak-sccs=RANGE).

  * autfilt learned --remove-unused-ap to remove atomic propositions
    that are declared in the input automaton, but not actually used.
    This of course makes sense only for input/output formats that
    declare atomic propositions (HOA & DSTAR).

  * autfilt learned two options to filter automata by count of used or
    unused atomic propositions: --used-ap=RANGE --unused-ap=RANGE.
    These differ from --ap=RANGE that only consider *declared* atomic
    propositions, regardless of whether they are actually used.

  * autfilt learned to filter automata by count of nondeterministsic
    states with --nondet-states=RANGE.

  * autfilt learned to filter automata representing stutter-invariant
    properties with --is-stutter-invariant.

  * autfilt learned two new options to highlight non-determinism:
    --highlight-nondet-states=NUM and --highlight-nondet-states=NUM
    where NUM is a color number.  Additionally --highlight-nondet=NUM is
    a shorthand for using the two.

  * autfilt learned to highlight a run matching a given word using the
    --highlight-word=[NUM,]WORD option.  However currently this only
    work on automata with Fin-less acceptance.

  * autfilt learned two options --generalized-rabin and
    --generalized-streett to convert the acceptance conditions.

  * genltl learned three new families: --dac-patterns=1..45,
    --eh-patterns=1..12, and --sb-patterns=1..27.  Unlike other options
    these do not output scalable patterns, but simply a list of formulas
    appearing in these three papers: Dwyer et al (FMSP'98), Etessami &
    Holzmann (Concur'00), Somenzi & Bloem (CAV'00).

  * genltl learned two options, --positive and --negative, to control
    wether formulas should be output after negation or not (or both).

  * The formater used by --format (for ltlfilt, ltlgrind, genltl,
    randltl) or --stats (for autfilt, dstar2tgba, ltl2tgba, ltldo,
    randaut) learned to recognize double-quoted fields and double the
    double-quotes output inbetween as expected from RFC4180-compliant
    CSV files.  For instance
      ltl2tgba -f 'a U "b+c"' --stats='"%f",%s'
    will output
      "a U ""b+c""",2

  * The --csv-escape option of genltl, ltlfilt, ltlgrind, and randltl
    is now deprecated.  The option is still here, but hidden and
    undocumented.

  * The --stats option of autfilt, dstar2tgba, ltl2tgba, ltldo,
    randaut learned to display the output (or input if that makes
    sense) automaton as a HOA one-liner using %h (or %H), helping to
    create CSV files contained automata.

  * autfilt and dstar2tgba learned to read automata from columns in
    CSV files, specified using the same filename/COLUMN syntax used by
    tools reading formulas.

  * Arguments passed to -x (in ltl2tgba, ltl2tgta, autfilt, dstar2tgba)
    that are not used are now reported as they might be typos.
    This ocurred a couple of times in our test-suite.  A similar
    check is done for the arguments of autfilt --sat-minimize=...

  Library:

  * The print_hoa() function will now output version 1.1 of the HOA
    format when passed the "1.1" option (i.e., use -H1.1 from any
    command-line tool).  As far as Spot is concerned, this allows
    negated properties to be expressed.  Version 1 of the HOA format
    is still the default, but we plan to default to version 1.1 in the
    future.

  * The "highlight-states" and "highlight-edges" named properties,
    which were introduced in 1.99.8, will now be output using
    "spot.highlight.edges:" and "spot.highlight.states:" headers if
    version 1.1 of the HOA format is selected.  The automaton parser
    was secretly able of reading that since 1.99.8, but that is now
    documented at https://spot.lrde.epita.fr/hoa.html#extensions

  * highlight_nondet_states() and highlight_nondet_edges() are
    new functions that define the above two named properties.

  * is_deterministic(), is_terminal(), is_weak(), and
    is_inherently_weak(), count_nondet_states(),
    highlight_nondet_edges(), highlight_nondet_states() will update
    the corresponding properties of the automaton as a side-effect of
    their check.

  * the sbacc() function, used by "ltl2tgba -S" and "autfilt -S" to
    convert automata to state-based acceptance, learned some tricks
    (using SCCs, pulling accepting marks common to all outgoing edges,
    and pushing acceptance marks common to all incoming edges) to
    reduce the number of additional states needed.

  * to_generalized_rabin() and to_generalized_streett() are two new
    functions that convert the acceptance condition as requested
    without changing the transition structure.

  * language_containment_checker now has default values for all
    parameters of its constructor.

  * spot::twa_run has a new method, project(), that can be used to
    project a run found in a product onto one of the original operand.
    This is for instance used by autfilt --highlight-word.

    The old spot::project_twa_run() function has been removed: it was
    not used anywhere in Spot, and had an obvious bug in its
    implementation, so it cannot be missed by anyone.

  * spot::twa has two new methods that supplement is_empty():
    twa::accepting_run() and twa::accepting_word().  They compute
    what their names suggest.  Note that twa::accepting_run(), unlike
    the two others, is currently restricted to automata with Fin-less
    acceptance.

  * spot::check_stutter_invariance() can now work on non-deterministic
    automata for which no corresponding formula is known.  This
    implies that "autfilt --check=stutter" will now label all
    automata, not just deterministic automata.

  * New LTL and PSL simplification rules:
    - if e is pure eventuality and g => e, then e U g = Fg
    - if u is purely universal and u => g, then u R g = Gg
    - {s[*0..j]}[]->b = {s[*1..j]}[]->b
    - {s[*0..j]}<>->b = {s[*1..j]}<>->b

  * spot::twa::succ_iterable renamed to
    spot::internal::twa_succ_iterable to make it clear this is not for
    public consumption.

  * spot::fair_kripke::state_acceptance_conditions() renamed to
    spot::fair_kripke::state_acceptance_mark() for consistency.  This
    is backward incompatible, but we are not aware of any actual use
    of this method.

  Python:

  * The __format__() method for formula supports the same
    operator-rewritting feature introduced in ltldo and ltlcross.
    So "{:[i]s}".format(f) is the same as
    "{:s}".format(f.unabbreviate("i")).

  * Bindings for language_containment_checker were added.

  * Bindings for randomize() were added.

  * Iterating over edges via "aut.out(s)" or "aut.edges()"
    now allows modifying the edge fields.

  * Under IPython the spot.ltsmin module now offers a
    %%pml magic to define promela models, compile them
    with spins, and dynamically load them.   This is
    akin to the %%dve magic that was already supported.

  * The %%dve and %%pml magics honor the SPOT_TMPDIR and
    TMPDIR environment variables.  This especially helps
    when the current directory is read-only.

  Documentation:

  * A new example page shows how to test the equivalence of
    two LTL/PSL formulas.  https://spot.lrde.epita.fr/tut04.html

  * A new page discusses explicit vs. on-the-fly interfaces for
    exploring automata in C++.  https://spot.lrde.epita.fr/tut50.html

  * Another new page shows how to implement an on-the-fly Kripke
    structure for a custom state space.
    https://spot.lrde.epita.fr/tut51.html

  * The concepts.html page now lists all named properties
    used by automata.

  Bug fixes:

  * When ltlcross found a bug using a product of complemented
    automata, the error message would report "Comp(Ni)*Comp(Pj)" as
    non-empty while the actual culprit was "Comp(Nj)*Comp(Pi)".

  * Fix some non-deterministic execution of minimize_wdba(), causing
    test-suite failures with the future G++ 7, and clang 3.9.

  * print_lbtt() had a memory leak when printing states without
    successors.

New in spot 2.0.3 (2016-07-11)

  Bug fixes:

  * The degen-lcache=1 option of the degeneralization algorithm (which
    is a default option) did not behave exactly as documented: instead
    of reusing the first level ever created for a state where the
    choice of the level is free, it reused the last level ever used.
    This caused some posterior simulation-based reductions to be less
    efficient at reducing automata (on the average).
  * The generalized testing automata displayed by the online
    translator were incorrect (those output by ltl2tgta were OK).
  * ltl2tgta should not offer options --ba, --monitor, --tgba and such.
  * the relabel() function could incorrectly unregister old atomic
    propositions even when they were still used in the output (e.g.,
    if a&p0 is relabeled to p0&p1).  This could cause ltldo and the
    online translator to report errors.

New in spot 2.0.2 (2016-06-17)

  Documentation:

  * We now have a citing page at https://spot.lrde.epita.fr/citing.html
    providing a list of references about Spot.
  * The Python examples have been augmented with the two examples
    from our ATVA'16 tool paper.

  Bug fixes:

  * Fix compilation error observed with Clang++ 3.7.1 and GCC 6.1.1
    headers.
  * Fix an infinite recursion in relabel_bse().
  * Various small typos and cosmetic cleanups.

New in spot 2.0.1 (2016-05-09)

  Library:

  * twa::unregister_ap() and twa_graph::remove_unused_ap() are new
    methods introduced to fix some of the bugs listed below.

  Documentation:

  * Add missing documentation for the option string passed to
    spot::make_emptiness_check_instantiator().

  * There is now a spot(7) man page listing all installed
    command-line tools.

  Python:

  * The tgba_determinize() function is now accessible in Python.

  Bug fixes:

  * The automaton parser would choke on comments like /******/.
  * check_strength() should also set negated properties.
  * Fix autfilt to apply --simplify-exclusive-ap only after
    the simplifications of (--small/--deterministic) have
    been performed.
  * The automaton parser did not fully register atomic propositions
    for automata read from never claim or as LBTT.
  * spot::ltsmin::kripke() had the same issue.
  * The sub_stats_reachable() function used to count the number
    of transitions based on the number of atomic propositions
    actually *used* by the automaton instead of using the number
    of AP declared.
  * print_hoa() will now output all the atomic propositions that have
    been registered, not only those that are used in the automaton.
    (Note that it will also throw an exception if the automaton uses
    an unregistered AP; this is how some of the above bugs were
    found.)
  * For Small or Deterministic preference, the postprocessor
    will now unregister atomic propositions that are no longer
    used in labels.   Simplification of exclusive properties
    and remove_ap::strip() will do similarly.
  * bench/ltl2tgba/ was not working since the source code
    reorganization of 1.99.7.
  * Various typos and minor documentation fixes.


New in spot 2.0 (2016-04-11)

  Command-line tools:

  * ltlfilt now also support the --accept-word=WORD and
    --reject-word=WORD options that were introduced in autfilt in the
    previous version.

  Python:

  * The output of spot.atomic_prop_collect() is printable and
    can now be passed directly to spot.ltsmin.model.kripke().

  Library:

  * digraph::valid_trans() renamed to digraph::is_valid_edge().

  Documentation:

  * The concepts page (https://spot.lrde.epita.fr/concepts.html) now
    includes a highlevel description of the architecture, and some
    notes aboute automata properties.

  * More Doxygen documentation for spot::formula and spot::digraph.

New in spot 1.99.9 (2016-03-14)

  Command-line tools:

  * autfilt has two new options: --accept-word=WORD and
    --reject-word=WORD for filtering automata that accept or reject
    some word.  The option may be used multiple times.

  Library:

  * The parse_word() function can be used to parse a lasso-shaped
    word and build a twa_word.  The twa_word::as_automaton()
    method can be used to create an automaton out of that.
  * twa::ap_var() renamed to twa::ap_vars().
  * emptiness_check_instantiator::min_acceptance_conditions() and
    emptiness_check_instantiator::max_acceptance_conditions() renamed
    to emptiness_check_instantiator::min_sets() and
    emptiness_check_instantiator::max_sets().
  * tgba_reachable_iterator (and subclasses) was renamed to
    twa_reachable_iterator for consistency.

  Documentation:

  * The page https://spot.lrde.epita.fr/upgrade2.html should help
    people migrating old C++ code written for Spot 1.2.x, and update
    it for (the upcoming) Spot 2.0.

  Bug fixes:

  * spot/twaalgos/gtec/gtec.hh was incorrectly installed as
  spot/tgbaalgos/gtec/gtec.hh.
  * The shared libraries should now compile again on Darwin.

New in spot 1.99.8 (2016-02-18)

  Command-line tools:

  * ltl2tgba now also support the --generic option (already supported
    by ltldo and autfilt) to lift any restriction on the acceptance
    condition produced.  This option now has a short version: -G.

  * ltl2tgba and autfilt have learnt how to determinize automata.
    For this to work, --generic acceptance should be enabled (this
    is the default for autfilt, but not for ltl2tgba).

    "ltl2tgba -G -D" will now always outpout a deterministic automaton.
    It can be an automaton with transition-based parity acceptance in
    case Spot could not find a deterministic automaton with (maybe
    generalized) Büchi acceptance.

    "ltl2tgba -D" is unchanged (the --tgba acceptance is the default),
    and will output a deterministic automaton with (generalized) Büchi
    acceptance only if one could be found.  Otherwise a
    non-deterministic automaton is output, but this does NOT mean that
    no deterministic Büchi automaton exist for this formula.  It only
    means Spot could not find it.

    "autfilt -D" will determinize any automaton, because --generic
    acceptance is the default for autfilt.

    "autfilt -D --tgba" will behave like "ltl2tgba -D", i.e., it may
    fail to find a deterministic automaton (even if one exists) and
    return a nondeterministic automaton.

  * "autfilt --complement" now also works for non-deterministic
    automata but will output a deterministic automaton.
    "autfilt --complement --tgba" will likely output a
    nondeterministic TGBA.

  * autfilt has a new option, --included-in, to filter automata whose
    language are included in the language of a given automaton.

  * autfilt has a new option, --equivalent-to, to filter automata
    that are equivalent (language-wise) to a given automaton.

  * ltlcross has a new option --determinize to instruct it to
    complement non-deterministic automata via determinization.  This
    option is not enabled by default as it can potentially be slow and
    generate large automata.  When --determinize is given, option
    --product=0 is implied, since the tests based on products with
    random state-space are pointless for deterministic automata.

  * ltl2tgba and ltldo now support %< and %> in the string passed
    to --stats when reading formulas from a CSV file.

  * ltlfilt's option --size-min=N, --size-max=N, --bsize-min=N, and
    --bsize-max=N have been reimplemented as --size=RANGE and
    --bsize=RANGE.  The old names are still supported for backward
    compatibility, but they are not documented anymore.

  * ltlfilt's option --ap=N can now take a RANGE as parameter.

  * autfilt now has a --ap=RANGE option to filter automata by number
    of atomic propositions.

  Library:

  * Building products with different dictionaries now raise an
    exception instead of using an assertion that could be disabled.