NEWS

New in spot 1.99.5a (not yet released)

  Nothing yet.

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
      automata in order to do batch processing.  This format can be
      output by all tools (since Spot 1.2.5) using the --hoa option,
      and it can be read by autfilt (by default) and ltlcross (using
      the %H specifier).  The current implementation does not support
      alternation.  Multiple initial states are converted into an
      extra initial state; complemented acceptance sets Inf(!x) are
      converted to Inf(x); explicit or implicit labels can be used;
      aliases are supported; "--ABORT--" can be used in a stream.

    - The above HOA parser can also parse never claims, and LBTT
      automata, so the never claim parser and the LBTT parser have
      been removed.  This implies that autfilt can input a mix of HOA,
      never claims, and LBTT automata.  ltlcross also use the same
      parser for all these output, and the old %T and %N specifiers
      have been deprecated and replaced by %O (for output).

    - While not all algorithms in the library are able to work with
      any acceptance condition supported by the HOA format, the
      following two new functions mitigate that:

      - remove_fin() takes a TωA whose accepting condition uses Fin(x)
	primitive, and produces an equivalent TωA without Fin(x):
	i.e., the output acceptance is a disjunction of generalized
	Büchi acceptance.  This type of acceptance is supported by
	SCC-based emptiness-check, for instance.

      - similarly, to_tgba() converts any TωA into an automaton with
	generalized-Büchi acceptance.

    - randomize() is a new algorithm that randomly reorders the states
      and transitions of an automaton.  It can be used from the
      command-line using "autfilt --randomize".

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

    - LTL/PSL formulas can include /* comments */.

    - PSL SEREs support a new operator [:*i..j], the iterated fusion.
      [:*i..j] is to the fusion operator ':' what [*i..j] is to the
      concatenation operator ';'.  For instance (a*;b)[:*3] is the
      same as (a*;b):(a*;b):(a*;b).  The operator [:+], is syntactic
      sugar for [:*1..], and corresponds to the operator ⊕ introduced
      by Dax et al. (ATVA'09).

    - GraphViz output now uses an horizontal layout by default, and
      also use circular states (unless the automaton has more than 100
      states, or uses named-states).  The --dot option of the various
      command-line tools takes an optional parameter to fine-tune the
      GraphViz output (including vertical layout, forced circular or
      elliptic states, named automata, SCC information, ordered
      transitions, and different ways to colorize the acceptance
      sets).  The environment variables SPOT_DOTDEFAULT and
      SPOT_DOTEXTRA can also be used to respectively provide a default
      argument to --dot, and add extra attributes to the output graph.

    - Never claims can now be output in the style used by Spin since
      version 6.2.4 (i.e., using do..od instead of if..fi, and with
      atomic statements for terminal acceptance).  The default output
      is still the old one for compatibility with existing tools.  The
      new style can be requested from command-line tools using option
      --spin=6 (or -s6 for short).

    - Support for building unambiguous automata.  ltl_to_tgba() has a
      new options to produce unambiguous TGBA (used by ltl2tgba -U as
      discussed above).   The function is_unambiguous() will check
      whether an automaton is unambigous, and this is used by
      autfilt --is-unmabiguous.

    - The SAT-based minimization algorithm for deterministic automata
      has been updated to work with ω-Automaton with any acceptance.
      The input and the output acceptance can be different, so for
      instance it is possible to create a minimal deterministic
      Streett automaton starting from a deterministic Rabin automaton.
      This functionnality is available via autfilt's --sat-minimize
      option.  See doc/userdoc/satmin.html for details.

    - The on-line interface at http://spot.lrde.epita.fr/trans.html
      can be used to check stutter-invariance of any LTL/PSL formula.

    - The on-line interface will work around atomic propositions not
      supported by ltl3ba.  (E.g. you can now translate F(A) or
      G("foo < bar").)

  * Noteworthy code changes

    - Boost is not used anymore.

    - Automata are now manipulated exclusively via shared pointers.

    - Most of what was called tgba_something is now called
      twa_something, unless it is really meant to work only for TGBA.
      This includes functions, classes, file, and directory names.
      For instance the class tgba originally defined in tgba/tgba.hh,
      has been replaced by the class twa defined in twa/twa.hh.

    - the tgba_explicit class has been completely replaced by a more
      efficient twa_graph class.  Many of the algorithms that were
      written against the abstract tgba (now twa) interface have been
      rewritten using twa_graph instances as input and output, making
      the code a lot simpler.

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

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

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

      Instead of the following syntax:

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

      We now prefer:

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

      And the above syntax is really just syntactic suggar for

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

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

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

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

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

      Instead of writing code like
        i->current_acceptance_conditions() == aut->all_acceptance_conditions()
      we now write
        aut->acc().accepting(i->current_acceptance_conditions())
      (Note that for accepting(x) to return something meaningful, x
      should be a set of acceptance sets visitied infinitely often.  So let's
      imagine that in the above example i is looking at a self-loop.)

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

    - All functions used for printing LTL/PSL formulas or automata
      have been renamed to print_something().  Likewise the various
      parsers should be called parse_something() (they haven't yet
      all been renamed).

    - All test suites under src/ have been merged into a single one in
      src/tests/.  The testing tool that was called
      src/tgbatest/ltl2tgba has been renamed as src/tests/ikwiad
      (short for "I Know What I Am Doing") so that users should be
      less tempted to use it instead of src/bin/ltl2tgba.

  * Removed features

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

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

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

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

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

    - Input and output in the old, Spot-specific, text format for
      TGBA, has been fully removed.  We now use HOA everywhere.  (In
      case you have a file in this format, install Spot 1.2.6 and use
      "src/tgbatest/ltl2tgba -H -X file" to convert the file to HOA.)

New in spot 1.2.6 (2014-12-06)

  * New features:

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

  * Bug fixes:

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

New in spot 1.2.5 (2014-08-21)

  * New features:

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

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

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

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

  * Documentation:

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

  * Bug fixes:

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

New in spot 1.2.4 (2014-05-15)

  * New features:

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

  * Bug fixes:

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

New in spot 1.2.3 (2014-02-11)

  * New features:

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

  * Bug fixes:

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

New in spot 1.2.2 (2014-01-24)

  * Bug fixes:

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

New in spot 1.2.1 (2013-12-11)

  * New features:

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

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

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

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

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

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

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

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

  * Bug fixes:

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

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

New in spot 1.2 (2013-10-01)

  * Changes to command-line tools:

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

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

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

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

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

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

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

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

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

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