NEWS

New in spot 2.1.2.dev (not yet released)

  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 time any
    task in a more precise way thanks to %R, %[LETTER]R option. User
    or system time, for children or parent, can be measured
    separately.  A typical use-case is "ltldo --stats='... %[c]R ...'
    ..." to measure the time spent in the tool ran by ltldo, excluding
    that of ltldo.  In all tools, the difference between %r
    (wall-clock time) and %R (process time) can also be used to detect
    unreliable measurements.

  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 ressorting 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 bisimulations-based
    reduction on deterministic automata, to save time.  As an example,
    this halves the run time of
       genltl --rv-counter=10 | ltl2tgba

  Bugs:

  * ltl2tgba was alway 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.

  * Compression could encode '6' and '22' in the same way. This issue
    only appears when using the compression from intvcomp.hh.

  * 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 (the default) on non-simplified
    automata.

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.

  * The load_ltsmin() function has been split in two.  Now you should
    first call ltsmin_model::load(filename) to create an ltsmin_model,
    and then call the ltsmin_model::kripke(...) method to create an
    automaton that can be iterated on the fly.  The intermediate
    object can be queried about the supported variables and their
    types.

  * print_dot() now accepts several new options:
    - use "<N" to specify a maximum number of states to output.
      Incomplete states are then marked appropriately.  For a quick
      example, compare
	ltl2tgba -D 'Ga | Gb | Gc' -d'<3'
      with
        ltl2tgba -D 'Ga | Gb | Gc' -d
    - use "C(color)" to specify the color to use for filling states.
    - use "#" to display the internal number of each transition
    - use "k" to use state-based labels when possible.  This is
      similar to the "k" option already supported by print_hoa(), and
      is useful when printing Kripke structures.

  * Option "k" is automatically used by print_dot() and print_hoa()
    when printing Kripke structures.

  * print_dot() also honnor two new automaton properties called
    "highlight-edges" and "highlight-states".  These are used to color
    a subset of edges or transitions.

  * There is a new tgba_determinize() function.  Despite its name, it
    in facts works on transition-based Büchi automaton, and will first
    degeneralize any automaton with generalized Büchi acceptance.

  * The twa_safra_complement class has been removed.  Use
    tgba_determinize() and dtwa_complement() instead.

  * The twa::transition_annotation() and
    twa::compute_support_conditions() methods have been removed.

  * The interface for all functions parsing formulas (LTL, PSL, SERE,
    etc.) has been changed to use an interface similar to the one used
    for parsing automata.  These function now return a parsed_formula
    object that includes both a formula and a list of syntax errors.

    Typically a function written as

       spot::formula read(std::string input)
       {
	  spot::parse_error_list pel;
	  spot::formula f = spot::parse_infix_psl(input, pel);
	  if (spot::format_parse_errors(std::cerr, input, pel))
	    exit(2);
	  return f;
       }

    should be updated to

       spot::formula read(std::string input)
       {
	  spot::parsed_formula pf = spot::parse_infix_psl(input);
	  if (pf.format_errors(std::cerr))
	    exit(2);
	  return pf.f;
       }

  Python:

  * The ltsmin interface has been binded in Python.  It also
    comes with a %%dve cell magic to edit DiVinE models in the notebook.
    See https://spot.lrde.epita.fr/ipynb/ltsmin.html for a short example.

  * spot.setup() sets de maximum number of states to display in
    automata to 50 by default, as more states is likely to be
    unreadable (and slow to process by GraphViz).  This can be
    overridden by calling spot.setup(max_states=N).

  * Automata now have methods to color selected states and
    transitions.  See
    https://spot.lrde.epita.fr/ipynb/highlighting.html for an example.

  Documentation:

  * There is a new page giving informal illustrations (and extra
    pointers) for some concepts used in Spot.
    See https://spot.lrde.epita.fr/concepts.html

  Bug fixes:

  * Using ltl2tgba -U would fail to output the unambiguous property
    (regression introduced in 1.99.7)
  * ltlfilt, autfilt, randltl, and randaut could easily crash when
    compiled statically (i.e., with configure --disable-shared).
  * "1 U (a | Fb)" was not always simplified to "F(a | b)".
  * destroying the operands of an otf_product() before the product
    itself could crash.

New in spot 1.99.7 (2016-01-15)

  Command-line tools:

  * BACKWARD INCOMPATIBLE CHANGE: All tools that output automata now
    use the HOA format by default instead of the GraphViz output.
    This makes it easier to pipe several commands together.

    If you have an old script that relies on GraphViz being the default
    output and that you do not want to update it, use
       export SPOT_DEFAULT_FORMAT=dot
    to get the old behavior back.

  * Tools that output automata now accept -d as a shorthand for --dot
    since requesting the GraphViz (a.k.a. dot) output by hand is now
    more frequent.
    randaut's short option for specifying edge-density used to be -d:
    it has been renamed to -e.

  * The SPOT_DEFAULT_FORMAT environment variable can be set to 'dot'
    or 'hoa' to force a default output format for automata.  Additional
    options may also be added, as in SPOT_DEFAULT_FORMAT='hoa=iv'.

  * autfilt has a new option: --is-inherently-weak.

  * The --check=strength option of all tools that produce automata
    will also test if an automaton is inherently weak.

  Library:

  * Installed headers now assume that they will be included as
    #include <spot/subdir/header.hh>
    instead of
    #include <subdir/header.hh>

    This implies that when Spot headers are installed in
    /usr/include/spot/... (the default when using the Debian packages)
    or /usr/local/include/spot/... (the default when compiling from
    source), then it is no longuer necessary to add
    -I/usr/include/spot or -I/usr/local/include/spot when compiling,
    as /usr/include and /usr/local/include are usually searched by
    default.

    Inside the source distribution, the subdirectory src/ has been
    renamed to spot/, so that the root of the source tree can also be
    put on the preprocessor's search path to compile against a
    non-installed version of Spot.  Similarly, iface/ltsmin/ has been
    renamed to spot/ltsmin/, so that installed and non-installed
    directories can be used similarly.

  * twa::~twa() is now calling
      get_dict()->unregister_all_my_variable(this);
    so this does not need to be done in any subclass.

  * is_inherently_weak_automaton() is a new function, and
    check_strength() has been modified to also check inherently weak
    automata.

  * decompose_strength() is now extracting inherently weak SCCs
    instead of just weak SCCs.  This gets rid of some corner cases
    that used to require ad hoc handling.

  * acc_cond::acc_code's methods append_or(), append_and(), and
    shift_left() have been replaced by operators |=, &=, <<=, and for
    completeness the operators |, &, and << have been added.

  * Several methods have been removed from the acc_cond
    class because they were simply redundant with the methods of
    acc_cond::mark_t, and more complex to use.

       acc_cond::marks(...)      -> use acc_cond::mark_t(...)
       acc_cond::sets(m)         -> use m.sets()
       acc_cond::has(m, u)       -> use m.has(u)
       acc_cond::cup(l, r)       -> use l | r
       acc_cond::cap(l, r)       -> use l & r
       acc_cond::set_minus(l, r) -> use l - r

    Additionally, the following methods/functions have been renamed:

       acc_cond::is_tt() -> acc_cond::is_t()
       acc_cond::is_ff() -> acc_cond::is_f()
       parse_acc_code()  -> acc_cond::acc_code(...)

  * Automata property flags (those that tell whether the automaton is
    deterministic, weak, stutter-invariant, etc.) are now stored using
    three-valued logic: in addition to "maybe"/"yes" they can now also
    represent "no".  This is some preparation for the upcomming
    support of the HOA v1.1 format, but it also saves time in some
    algorithms (e.g, is_deterministic() can now return immediately on
    automata marked as not deterministic).

  * The automaton parser now accept negated properties as they will be
    introduced in HOA v1.1, and will check for some inconsistencies.
    These properties are stored and used when appropriate, but they
    are not yet output by the HOA printer.

  Python:

  * Iterating over the transitions leaving a state (the
    twa_graph::out() C++ function) is now possible in Python.  See
    https://spot.lrde.epita.fr/tut21.html for a demonstration.

  * Membership to acceptance sets can be specified using Python list
    when calling for instance the Python version of twa_graph::new_edge().
    See https://spot.lrde.epita.fr/tut22.html for a demonstration.

  * Automaton states can be named via the set_state_names() method.
    See https://spot.lrde.epita.fr/ipynb/product.html for an example.

  Documentation:

  * There is a new page explaining how to compile example programs and
    and link them with Spot.  https://spot.lrde.epita.fr/compile.html

  * Python bindings for manipulating acceptance conditions are
    demonstrated by https://spot.lrde.epita.fr/ipynb/acc_cond.html,
    and a Python implementation of the product of two automata is
    illustrated by https://spot.lrde.epita.fr/ipynb/product.html

  Source code reorganisation:

  * A lot of directories have been shuffled around in the
    distribution:
      src/                   ->  spot/    (see rational above)
      iface/ltsmin/  (code)  ->  spot/ltsmin/
      wrap/python/           ->  python/
      src/tests/             ->  tests/core/
      src/sanity/            ->  tests/sanity/
      iface/ltsmin/  (tests) ->  tests/ltsmin/
      wrap/python/tests      ->  tests/python/

  Bug fixes:

  * twa_graph would incorrectly replace named-states during
    purge_dead_states and purge_unreachable_states.
  * twa::ap() would contain duplicates when an atomic proposition
    was registered several times.
  * product() would incorrectly mark the product of two
    sttuter-sensitive automata as stutter-sensitive as well.
  * complete() could incorrectly reuse an existing (but accepting!)
    state as a sink.

New in spot 1.99.6 (2015-12-04)

  Command-line tools:

  * autfilt has two new filters: --is-weak and --is-terminal.

  * autfilt has a new transformation: --decompose-strength,
    implementing the decomposition of our TACAS'13 paper.
    A demonstration of this feature via the Python bindings
    can be found at https://spot.lrde.epita.fr/ipynb/decompose.html

  * All tools that output HOA files accept a --check=strength option
    to request automata to be marked as "weak" or "terminal" as
    appropriate.  Without this option, these properties may only be
    set as a side-effect of running transformations that use this
    information.

  Library:

  * Properties of automata (like the "properties:" line of the HOA
    format) are stored as bits whose interpretation is True=yes,
    False=maybe.  Having getters like "aut->is_deterministic()" or
    "aut->is_unambiguous()" was confusing, because there are separate
    functions "is_deterministic(aut)" and "is_unambiguous(aut)" that
    do actually check the automaton.  The getters have been renamed to
    avoid confusion, and get names more in line with the HOA format.

    - twa::has_state_based_acc() -> twa::prop_state_acc()
    - twa::prop_state_based_acc(bool) -> twa::prop_state_acc(bool)
    - twa::is_inherently_weak() -> twa::prop_inherently_weak()
    - twa::is_deterministic() -> twa::prop_deterministic()
    - twa::is_unambiguous() -> twa::prop_unambiguous()
    - twa::is_stutter_invariant() -> twa::prop_stutter_invariant()
    - twa::is_stutter_sensitive() -> twa::prop_stutter_sensitive()

    The setters have the same names as the getters, except they take a
    Boolean argument.  This argument used to be optionnal (defaulting
    to True), but it no longer is.

  * Automata now support the "weak" and "terminal" properties in
    addition to the previously supported "inherently-weak".

  * By default the HOA printer tries not to bloat the output with
    properties that are redundant and probably useless.  The HOA
    printer now has a new option "v" (use "-Hv" from the command line)
    to output more verbose "properties:".  This currently includes
    outputing "no-univ-branch", outputting "unambiguous" even for
    automata already tagged as "deterministic", and "inherently-weak"
    or "weak" even for automata tagged "weak" or "terminal".

  * The HOA printer has a new option "k" (use "-Hk" from the command
    line) to output automata using state labels whenever possible.
    This is useful to print Kripke structures.

  * The dot output will display pair of states when displaying an
    automaton built as an explicit product.  This works in IPython
    with spot.product() or spot.product_or() and in the shell with
    autfilt's --product or --product-or options.

  * The print_dot() function supports a new option, +N, where N is a
    positive integer that will be added to all set numbers in the
    output.  This is convenient when displaying two automata before
    building their product: use +N to shift the displayed sets of the
    second automaton by the number of acceptance sets N of the first
    one.

  * The sat minimization for DTωA now does a better job at selecting
    reference automata when the output acceptance is the the same as
    the input acceptance.  This can provide nice speedups when tring
    to syntethise larged automata with different acceptance
    conditions.

  * Explicit Kripke structures (i.e., stored as explicit graphs) have
    been rewritten above the graph class, using an interface similar
    to the twa class.  The new class is called kripke_graph.  The ad
    hoc Kripke parser and printer have been removed, because we can
    now use print_hoa() with the "k" option to print Kripke structure
    in the HOA format, and furthermore the parse_aut() function now
    has an option to load such an HOA file as a kripke_graph.

  * The HOA parser now accepts identifier, aliases, and headernames
    containing dots, as this will be allowed in the next version of
    the HOA format.

  * Renamings:
    is_guarantee_automaton() -> is_terminal_automaton()
    tgba_run -> twa_run
    twa_word::print -> operator<<
    dtgba_sat_synthetize() -> dtwa_sat_synthetize()
    dtgba_sat_synthetize_dichotomy() -> dtwa_sat_synthetize_dichotomy()

  Python:

  * Add bindings for is_unambiguous().
  * Better interface for sat_minimize().

  Bug fixes:

  * the HOA parser was ignoring the "unambiguous" property.
  * --dot=Bb should work like --dot=b, allowing us to disable
    a B option set via an environment variable.

New in spot 1.99.5 (2015-11-03)

  Command-line tools:

  * autfilt has gained a --complement option.
    It currently works only for deterministic automata.

  * By default, autfilt does not simplify automata (this has not
    changed), as if the --low --any options were used.  But now, if
    one of --small, --deterministic, or --any is given, the
    optimization level automatically defaults to --high (unless
    specified otherwise).  For symmetry, if one of --low, --medium, or
    --high is given, then the translation intent defaults to --small
    (unless specified otherwise).

  * autfilt, dstar2tgba, ltlcross, and ltldo now trust the (supported)
    automaton properties declared in any HOA file they read.  This can
    be disabled with option --trust-hoa=no.

  * ltlgrind FILENAME[/COL] is now the same as
    ltlgrind -F FILENAME[/COL] for consistency with ltlfilt.

  Library:

  * dtgba_complement() was renamed to dtwa_complement(), moved to
    complement.hh, and its purpose was restricted to just completing
    the automaton and complementing its acceptance condition.  Any
    further acceptance condition transformation can be done with
    to_generalized_buchi() or remove_fin().

  * The remove_fin() has learnt how to better deal with automata that
    are declared as weak.  This code was previously in
    dtgba_complement().

  * scc_filter_states() has learnt to remove useless acceptance marks
    that are on transitions between SCCs, while preserving state-based
    acceptance.  The most visible effect is in the output of "ltl2tgba
    -s XXXa": it used to have 5 accepting states, it now has only one.
    (Changing removing acceptance of those 4 states has no effect on
    the language, but it speeds up some algorithms like NDFS-based
    emptiness checks, as discussed in our Spin'15 paper.)

  * The HOA parser will diagnose any version that is not v1, unless it
    looks like a subversion of v1 and no parse error was detected.

  * The way to pass option to the automaton parser has been changed to
    make it easier to introduce new options.  One such new option is
    "trust_hoa": when true (the default) supported properties declared
    in HOA files are trusted even if they cannot be easily be verified.
    Another option "raise_errors" now replaces the method
      automaton_stream_parser::parse_strict().

  * The output of the automaton parser now include the list of parse
    errors (that does not have to be passed as a parameters) and the
    input filename (making the output of error messages easier).

  * The following renamings make the code more consistent:
    ltl_simplifier -> tl_simplifier
    tgba_statistics::transitions -> twa_statistics::edges
    tgba_sub_statistics::sub_transitions -> twa_sub_statistics::transitions
    tgba_run -> twa_run
    reduce_run -> twa_run::reduce
    replay_tgba_run -> twa_run::replay
    print_tgba_run -> operator<<
    tgba_run_to_tgba -> twa_run::as_twa
    format_parse_aut_errors -> parsed_aut::format_errors
    twa_succ_iterator::current_state -> twa_succ_iterator::dst
    twa_succ_iterator::current_condition -> twa_succ_iterator::cond
    twa_succ_iterator::current_acceptance_conditions -> twa_succ_iterator::acc
    ta_succ_iterator::current_state -> ta_succ_iterator::dst
    ta_succ_iterator::current_condition -> ta_succ_iterator::cond
    ta_succ_iterator::current_acceptance_conditions -> ta_succ_iterator::acc

  Python:

  * The minimum supported Python version is now 3.3.
  * Add bindings for complete() and dtwa_complement()
  * Formulas now have a custom __format__ function.  See
    https://spot.lrde.epita.fr/tut01.html for examples.