NEWS

New in spot 2.0a (not yet released)

  Command-line tools:

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

  * autfilt has several new options 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).

  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.

  Documentation:

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

  Python:

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

  Bug fixes:

  * Typo in documentation of the -H option in --help output.
  * 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.
  * 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.

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.
  * The Debian package is now compiled for all Python3 versions
    supported by Debian, not just the default one.
  * Automata now have get_name()/set_name() methods.
  * spot.postprocess(aut, *options), or aut.postprocess(*options)
    simplify the use of the spot.postprocessor object.  (Just like we
    have spot.translate() on top of spot.translator().)
  * spot.automata() and spot.automaton() now have additional
    optional arguments:
    - timeout: to restrict the runtime of commands that
      produce automata
    - trust_hoa: can be set to False to ignore HOA properties
      that cannot be easily verified
    - ignore_abort: can be set to False if you do not want to
      skip automata ended with --ABORT--.

  Documentation:

  * There is a new page showing how to use spot::postprocessor
    to convert any type of automaton to Büchi.
    https://spot.lrde.epita.fr/tut30.html

  Bugs fixed:

  * Work around some weird exception raised when using the
    randltlgenerator under Python 3.5.
  * Recognize "nullptr" formulas as None in Python.
  * Fix compilation of bench/stutter/
  * Handle saturation of formula reference counts.
  * Fix typo in the Python code for the CGI server.
  * "randaut -Q0 1" used to segfault.
  * "ltlgrind -F FILENAME/COL" did not preserve other CSV columns.
  * "ltlgrind --help" did not document FORMAT.
  * unabbreviate could easily use forbidden operators.
  * "autfilt --is-unambiguous" could fail to detect the nonambiguity
    of some automata with empty languages.
  * When parsing long tokens (e.g, state labels representing
    very large strings) the automaton parser could die with
    "input buffer overflow, can't enlarge buffer because scanner uses REJECT"

New in spot 1.99.4 (2015-10-01)

  New features:

  * autfilt's --sat-minimize now takes a "colored" option to constrain
    all transitions (or states) in the output automaton to belong to
    exactly one acceptance sets.  This is useful when targeting parity
    acceptance.

  * autfilt has a new --product-or option.  This builds a synchronized
    product of two (completed of needed) automata in order to
    recognize the *sum* of their languages.  This works by just using
    the disjunction of their acceptance conditions (with appropriate
    renumbering of the acceptance sets).

    For consistency, the --product option (that builds a synchronized
    product that recognizes the *intersection* of the languages) now
    also has a --product-and alias.

  * the parser for ltl2dstar's format has been merged with the parser
    for the other automata formats.  This implies two things:
    - autfilt and dstar2tgba (despite its name) can now both read
      automata written in any of the four supported syntaxes
      (ltl2dstar's, lbtt's, HOA, never claim).
    - "dstar2tgba some files..." now behaves exactly like
      "autfilt --tgba --high --small some files...".
      (But dstar2tgba does not offer all the filtering and
      transformations options of autfilt.)

  Major code changes and reorganization:

  * The class hierarchy for temporal formulas has been entirely
    rewritten.  This change is actually quite massive (~13200 lines
    removed, ~8200 lines added), and brings some nice benefits:
    - LTL/PSL formulas are now represented by lightweight formula
      objects (instead of pointers to children of an abstract
      formula class) that perform reference counting automatically.
    - There is no hierachy anymore: all operators are represented by
      a single type of node in the syntax tree, and an enumerator is
      used to distinguish between operators.
    - Visitors have been replaced by member functions such as map()
      or traverse(), that take a function (usually written as a
      lambda function) and apply it to the nodes of the tree.
    - As a consequence, writing algorithms that manipulate formula
      is more friendly, and several algorithms that spanned a few
      pages have been reduced to a few lines.
    The page https://spot.lrde.epita.fr/tut03.html illustrates the
    new interface, in both C++ and Python.

  * Directories ltlast/, ltlenv/, and ltlvisit/, have been merged into
    a single tl/ directory (for temporal logic).  This is motivated by
    the fact that these formulas are not restricted to LTL, and by the
    fact that we no longuer use the "visitor" pattern.

  * The LTL/PSL parser is now declared in tl/parse.hh (instead of
    ltlparse/public.hh).

  * The spot::ltl namespace has been merged with the spot namespace.

  * The dupexp_dfs() function has been renamed to copy(), and has
    learned to preserve named states if required.

  * Atomic propositions can be declared without going through an
    environment using the spot::formula::ap() static function.  They
    can be registered for an automaton directly using the
    spot::twa::register_ap() method.  The vector of atomic
    propositions used by an automaton can now be retrieved using the
    spot::twa::ap() method.

New in spot 1.99.3 (2015-08-26)

  * The CGI script for LTL translation offers a HOA download link
    for each generated automaton.

  * The html documentation now includes a HTML copies of the man
    pages, and HTML copies of the Python notebooks.

  * scc_filter(aut, true) does not remove Fin marks from rejecting
    SCCs, but it now does remove Fin marks from transitions between
    SCCs.

  * All the unabbreviation functions (unabbreviate_ltl(),
    unabbreviate_logic(), unabbreviate_wm()) have been merged into a
    single unabbreviate() function that takes a string representing
    the list of operators to remove among "eFGiMRW^" where 'e', 'i',
    and '^' stand respectively for <->, ->, and xor.
    This feature is also available via ltlfilt --unabbreviate.

  * In LTL formulas, atomic propositions specified using double-quotes
    can now include \" and \\.  (This is more consistent with the HOA
    format, which already allows that.)

  * All the conversion routines that were written specifically for
    ltl2dstar's output format (DRA->BA & DRA->TGBA) have been ported
    to the new TωA structure supporting the HOA format.  The DRA->TGBA
    conversion was reimplemented in the previous release, and the
    DRA->BA conversion has been reimplemented in this release (but it
    is still restricted to state-based acceptance).  All these
    conversions are called automatically by to_generalized_buchi()
    or remove_fin() so there should be no need to call them directly.

    As a consequence:
    - "autfilt --remove-fin" or "autfilt -B" is better at converting
      state-based Rabin automata: it will produce a DBA if the input is
      deterministic and DBA-realizable, but will preserve as much
      determinism as possible otherwise.
    - a lot of obsolete code that was here only to support the old
      conversion routines has been removed.  (The number of lines
      removed by this release is twice the number of lines added.)
    - ltlcross now uses automata in ltl2dstar's format directly,
      without converting them to Büchi (this makes the statistics
      reported in CSV files more relevant).
    - ltlcross no longer outputs additional columns about the size
      of the input automaton in the case ltl2dstar's format is used.
    - ltldo uses results in ltl2dstar's format directly, without
      converting them to Büchi.
    - dstar2tgba has been greatly simplified and now uses the
      same output routines as all the other tools that output
      automata.  This implies a few minor semantic changes, for
      instance --stats=%A used to output the number of acceptance
      *pairs* in the input automaton, while it now outputs the
      number of acceptance sets like in all the other tools.

  * Bugs fixed
    - Some acceptance conditions like Fin(0)|Fin(1)|Fin(2)&Inf(3)
      were not detected as generalized-Rabin.
    - Unknown arguments for print_hoa() (i.e., option -H in command-line
      tools) are now diagnosed.
    - The CGI script for LTL translation now forces transition-based
      acceptance on WDBA-minimized automata when TGBA is requested.
    - ltlgrind --help output had some options documented twice, or
      in the wrong place.
    - The man page for ltlcross had obsolete examples.
    - When outputting atomic propositions in double quotes, the
      escaping routine used by the two styles of LaTeX output was
      slightly wrong.  For instance ^ was incorrectly escaped, and
      the double quotes where not always properly rendered.
    - A spurious assertion was triggered by streett_to_generalized_buchi(),
      but only when compiled in DEBUG mode.
    - LTL formula rewritten in Spin's syntax no longer have their ->
      and <-> rewritten away.
    - Fix some warnings reported by the development version of GCC 6.
    - The spot.translate() function of the Python binding had a typo
      preventing the use of 'low'/'medium'/'high' as argument.
    - Fix spurious failure of uniq.test under different locales.
    - ltlcross now recovers from out-of-memory errors during
      state-space products.
    - bitvect.test was failing on 32bit architectures with
      assertions enabled because of a bug in the test case.

New in spot 1.99.2 (2015-07-18)

  * The scc_info object, used to build a map of SCCs while gathering
    additional information, has been simplified and speed up.  One
    test case where ltlcross would take more than 13min (to check the
    translation of one PSL formula) now takes only 75s.

  * streett_to_generalized_buchi() is a new function that implements
    what its name suggests, with some SCC-based optimizations over the
    naive definition.  It is used by the to_generalized_buchi() and
    remove_fin() functions when the input automaton is a Streett
    automaton with more than 3 pairs (this threeshold can be changed
    via the SPOT_STREETT_CONV_MIN environment variable -- see the
    spot-x(7) man page for details).

    This is mainly useful to ltlcross, which has to get rid of "Fin"
    acceptance to perform its checks.  As an example, the Streett
    automaton generatated by ltl2dstar (configured with ltl2tgba) for
    the formula
      !((GFa -> GFb) & (GFc -> GFd))
    has 4307 states and 14 acceptance sets.  The new algorithm can
    translate it into a TGBA with 9754 states and 7 acceptance sets,
    while the default approch used for converting any acceptance
    to TGBA would produce 250967 states and 7 acceptance sets.

  * Bugs fixed:
    - p[+][:*2] was not detected as belonging to siPSL.
    - scc_filter() would incorrectly remove Fin marks from
      rejecting SCCs.
    - the libspotltsmin library is installed.
    - ltlcross and ltldo did not properly quote atomic propositions
      and temporary file names containing a single-quote.
    - a missing Python.h is now diagnosed at ./configure time, with
      the suggestion to either install python3-devel, or run
      ./configure --disable-python.
    - Debian packages for libraries have been split from
      the main Spot package, as per Debian guidelines.

New in spot 1.99.1 (2015-06-23)

  * Major changes motivating the jump in version number

    - Spot now works with automata that can represent more than
      generalized Büchi acceptance.  Older versions were built around
      the concept of TGBA (Transition-based Generalized Büchi
      Automata) while this version now deals with what we call TωA
      (Transition-based ω-Automata).  TωA support arbitrary acceptance
      conditions specified as a Boolean formula of transition sets
      that must be visited infinitely often or finitely often.  This
      genericity allows for instance to represent Rabin or Streett
      automata, as well as some generalized variants of those.

    - Spot has near complete support for the Hanoi Omega Automata
      format.  http://adl.github.io/hoaf/  This formats supports
      automata with the generic acceptance condition described above,
      and has been implemented in a number of third-party tools (see
      http://adl.github.io/hoaf/support.html) to ease their
      interactions.  The only part of the format not yet implemented in
      Spot is the support for alternating automata.

    - Spot is now compiling in C++11 mode.  The set of C++11 features
      we use requires GCC >= 4.8 or Clang >= 3.5.  Although GCC 4.8 is
      more than 2-year old, people with older installations won't be
      able to install this version of Spot.

    - As a consequence of the switches to C++11 and to TωA, a lot of
      the existing C++ interfaces have been renamed, and sometime
      reworked.  This makes this version of Spot not backward
      compatible with Spot 1.2.x.  See below for the most important
      API changes.  Furtheremore, the reason this release is not
      called Spot 2.0 is that we have more of those changes planned.

    - Support for Python 2 was dropped.  We now support only Python
      3.2 or later.  The Python bindings have been improved a lot, and
      include some conveniance functions for better integration with
      IPython's rich display system.  User familiar with IPython's
      notebook should have a look at the notebook files in
      wrap/python/tests/*.ipynb

  * Major news for the command-line tools

    - The set of tools installed by spot now consists in the following
      11 commands.  Those marked with a '+' are new in this release.

      - randltl    Generate random LTL/PSL formulas.
      - ltlfilt    Filter and convert LTL/PSL formulas.
      - genltl     Generate LTL formulas from scalable patterns.
      - ltl2tgba   Translate LTL/PSL formulas into Büchi automata.
      - ltl2tgta   Translate LTL/PSL formulas into Testing automata.
      - ltlcross   Cross-compare LTL/PSL-to-Büchi translators.
      + ltlgrind   Mutate LTL/PSL formula.
      - dstar2tgba Convert deterministic Rabin or Streett automata into Büchi.
      + randaut    Generate random automata.
      + autfilt    Filter and convert automata.
      + ltldo      Run LTL/PSL formulas through other tools.

      randaut does not need any presentation: it does what you expect.

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

      autfilt is a new tool that processes a stream of automata.  It
      allows format conversion, filtering automata based on some
      properties, and general transformations (e.g., change of
      acceptance conditions, removal of useless states, product
      between automata, etc.).

      ltldo is a new tool that runs LTL/PSL formulas through other
      tools, but uses Spot's command-line interfaces for specifying
      input and output.  This makes it easier to use third-party tool
      in a pipe, and it also takes care of some necessary format
      conversion.

    - ltl2tgba has a new option, -U, to produce unambiguous automata.
      In unambiguous automata any word is recognized by at most one
      accepting run, but there might be several ways to reject a word.
      This works for LTL and PSL formulas.

    - ltl2tgba has a new option, -S, to produce generalized-Büchi
      automata with state-based acceptance.  Those are obtained by
      converting some transition-based GBA into a state-based GBA, so
      they are usually not as small as one would wish.  The same
      option -S is also supported by autfilt.

    - ltlcross will work with translator producing automata with any
      acceptance condition, provided the output is in the HOA format.
      So it can effectively be used to validate tools producing Rabin
      or Streett automata.

    - ltlcross has several new options:

        --grind attempts to reduce the size of any bogus formula it
        discovers, while still exhibiting the bug.

        --ignore-execution-failures ignores cases where a translator
        exits with a non-zero status.

	--automata save the produced automata into the CSV or JSON
        file.  Those automata are saved using the HOA format.

      ltlcross will also output two extra columns in its CSV/JSON
      output: "ambiguous_aut" and "complete_aut" are Boolean
      that respectively tells whether the automaton is
      ambiguous and complete.

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

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

    - ltlfilt's old -n/--negate option can only be used as --negate
      now.  The short '-n NUM' option is now the same as the new
      --max-count=N option, for consistency with other tools.

    - ltlfilt has a new --count option to count the number of matching
      automata.

    - ltlfilt has a new --exclusive-ap option to constrain formulas
      based on a list of mutually exclusive atomic propositions.

    - ltlfilt has a new option --define to be used in conjunction with
      --relabel or --relabel-bool to print the mapping between old and
      new labels.

    - all tools that produce formulas or automata now have an --output
      (a.k.a. -o) option to redirect that output to a file instead of
      standard output.  The name of this file can be constructed using
      the same %-escape sequences that are available for --stats or
      --format.

    - all tools that output formulas have a -0 option to separate
      formulas with \0.  This helps in conjunction with xargs -0.

    - all tools that output automata have a --check option that
      request extra checks to be performed on the output to fill
      in properties values for the HOA format.  This options
      implies -H for HOA output.  For instance
      	ltl2tgba -H 'formula'
      will declare the output automaton as 'stutter-invariant'
      only if the formula is syntactically stutter-invariant
      (e.g., in LTL\X).  With
        ltl2tgba --check 'formula'
      additional checks will be performed, and the automaton
      will be accurately marked as either 'stutter-invariant'
      or 'stutter-sensitive'.  Another check performed by
      --check is testing whether the automaton is unambiguous.

    - ltlcross (and ltldo) have a list of hard-coded shorthands
      for some existing tools.  So for instance running
      'ltlcross spin ...' is the same as running
      'ltlcross "spin -f %s>%N" ...'.   This feature is much
      more useful for ltldo.

    - For options that take an output filename (i.e., ltlcross's
      --save-bogus, --grind, --csv, --json) you can force the file
      to be opened in append mode (instead of being truncated) by
      by prefixing the filename with ">>".  For instance
      	  --save-bogus=">>bugs.ltl"
      will append to the end of the file.

  * Other noteworthy news

    - The web site moved to http://spot.lrde.epita.fr/.

    - We now have Debian packages.
      See http://spot.lrde.epita.fr/install.html

    - The documentation now includes some simple code examples
      for both Python and C++.  (This is still a work in progress.)

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

    - There is a parser for the HOA format
      (http://adl.github.io/hoaf/) available as a
      spot::automaton_stream_parser object or spot::parse_aut()
      function.  The former version is able to parse a stream of