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New in spot 2.4.1.dev (not yet released)
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  Tools:

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  - genltl learned to generate a new family of formulas, taken from
    the SYNTCOMP competition on reactive synthesis:
    --gf-equiv=RANGE      (GFa{1} & GFa{2} & ... & GFa{n}) <-> GFz

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  - genltl learned to generate 4 new families of formulas, taken
    from Müller & Sickert's GandALF'17 paper:
    --ms-example=RANGE     GF(a1&X(a2&X(a3&...)))&F(b1&F(b2&F(b3&...)))
    --ms-phi-h=RANGE       FG(a|b)|FG(!a|Xb)|FG(a|XXb)|FG(!a|XXXb)|...
    --ms-phi-r=RANGE       (FGa{n}&GFb{n})|((FGa{n-1}|GFb{n-1})&(...))
    --ms-phi-s=RANGE       (FGa{n}|GFb{n})&((FGa{n-1}&GFb{n-1})|(...))
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  - autfilt learned --streett-like to convert an automaton in order to
    have a Streett-like acceptance condition. It only works with
    ω-automata having an acceptance in disjunctive normal form.

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  - autfilt learned --dca to convert a Streett-like automaton or an
    automaton with an acceptance in disjunctive normal form to a
    deterministic co-Büchi automaton using the new functions
    [nsa-dnf]_to_dca() described below.

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  - ltlfilt learned to measure wall-time using --format=%r.

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

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  - ltlsynt is a new tool for synthesizing AIGER circuits from LTL/PSL
    formulas.

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  - ltldo learned to limit the number of automata it outputs using -n.

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  - autcross, ltlcross, and ltldo learned --fail-on-timeout.

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  - The new -x tls-impl=N option allows to fine-tune the
    implication-based simplification rules of ltl2tgba.  See the
    spot-x man-page for details.

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  Library:

  - Rename three methods of spot::scc_info. New names are clearer. The
    old names have been deprecated.

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  - scc_info now takes an optional argument to disable some feature
    that are expansive and not always necessary.  By default scc_info
    tracks the list of all states that belong to an SCC (you may now
    ask it not to), tracks the successor SCCs of each SCC (that can
    but turned off), and explores all SCCs of the automaton (you may
    request to stop on the first SCC that is found accepting).

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  - The new function scc_info::states_on_acc_cycle_of() is able to
    return all states visited by any accepting cycles of the
    specified SCC. It must only be called on automata with a
    Streett-like acceptance condition.

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  - The new function dnf_to_streett() is able to convert any automaton
    with an acceptance condition in Disjunctive Normal Form to a
    Streett-like automaton. This is used by the new option
    '--streett-like' of autfilt.

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  - The new functions spot::nsa_to_[nca-dca]()
    (or spot::dnf_to_[nca-dca]()) are able to convert when possible a
    Streett-like automaton (or any automaton with an acceptance in DNF)
    to an equivalent 'nca' (nondeterministic co-Büchi automaton) or
    'dca' (deterministic co-Büchi automaton).  Actually the resulting
    automaton will always recognize at least the same language.  It can
    recognize more if the original language can not be expressed with
    a co-Büchi acceptance condition.
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  - The new functions spot::is_recurrence() and spot::is_persistence()
    check respectively if a formula f belongs to the recurrence or
    persistence class. Two algorithms are available, one that
    checks if a formula is cobuchi_realizable (then it belongs to the
    persistence class) and the other that checks if it is
    detbuchi_realizable (then it belongs to the recurrence class).
    Force one method or the other by setting the environment variable
    SPOT_PR_CHECK to 1 or 2.
    Note that thanks to the duality of both classes, both algorithms
    will work either on f or its negation.
    (see https://spot.lrde.epita.fr/hierarchy.html for details).
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  - The new function spot::is_colored() checks if an automaton is colored
    (i.e., every transition belongs to exactly one acceptance set)

  - The new function spot::change_parity() can convert an automaton with parity
    acceptance condition to an equivalent automaton with another type of parity
    acceptance condition. The type of a parity acceptance condition states
    whether it is an odd or even parity acceptance condition, and whether it is
    a min or max parity acceptance condition.

  - The new function spot::colorize_parity() can colorize an automaton with
    a parity acceptance condition. The resulting automaton is a parity automaton
    and every transition belongs to exactly one acceptance set.

  - The new function spot::cleanup_parity_acceptance() can simplify the
    acceptance condition of an automaton with parity acceptance condition. It
    removes the unused acceptance sets and merges acceptance sets to keep the
    parity acceptance condition.

  - The new functions spot::parity_product() and spot::parity_product_or()
    compute respectively the intersection and the union of two automata with
    parity acceptance condition and keep the parity acceptance condition.

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  - The new function spot::remove_univ_otf() removes universal
    transitions on the fly from an alternating Büchi automaton
    using Miyano and Hayashi's breakpoint algorithm.

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  - In some cases, spot::degeneralize() would output Büchi automata
    with more SCCs than its input.  This was hard to notice, because
    very often simulation-based simplifications remove those extra
    SCCs.  This situation is now detected by spot::degeneralized() and
    fixed before returning the automaton.  A new optionnal argument
    can be passed to disable this behavior (or use -x degen-remscc=0
    from the command-line).

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  - In addition to detecting stutter-invariant formulas/automata, some
    can now study a stutter-sensitive automaton and detect the subset
    of states that are stutter-invariant.  See
    https://spot.lrde.epita.fr/ipynb/stutter-inv-states.html for
    examples.

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  Deprecation notices:

  (These functions still work but compilers emit warnings.)

  - spot::scc_info::used_acc(), spot::scc_info::used_acc_of() and
    spot::scc_info::acc() are deprecated. They have been renamed
    spot::scc_info::marks(), spot::scc_info::marks_of() and
    spot::scc_info::acc_sets_of() respectively.

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  Bugs fixed:

  - Automata produced by "genaut --ks-nca=N" were incorrectly marked
    as not complete.

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  - Fix some cases for which the highest setting of formulas
    simplification would produce worse results than lower settings.

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New in spot 2.4.1 (2017-10-05)
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  Bugs fixed:

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  - The formula class failed to build {a->c[*]} although it is
    allowed by our grammar.
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  - spot::scc_info::determine_unknown_acceptance() incorrectly
    considered some rejecting SCC as accepting.

  - spot::streett_to_generalized_buchi() could generate automata with
    empty language if some Fin set did not intersect all accepting
    SCCs.  As a consequence, some Streett-like automata were
    considered empty even though they were not.  Also, the same
    function could crash on input that had a Streett-like acceptance
    not using all declared sets.

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  - The twa_graph::merge_edges() function relied on BDD IDs to sort
    edges.  This in turn caused some algorithms (like the
    degeneralization) to produce slighltly different (but still correct)
    outputs depending on the BDD operations performed before.
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  - spot::simulation() could incorrectly flag an automaton as
    non-deterministic.
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New in spot 2.4 (2017-09-06)
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  Build:

  - Spot is now built in C++14 mode, so you need at least GCC 5 or
    clang 3.4.  The current version of all major linux distributions
    ship with at least GCC 6, which defaults to C++14, so this should
    not be a problem.  In *this* release of Spot, most of the header
    files are still C++11 compatible, so you should be able to include
    Spot in a C++11 project in case you do not yet want to upgrade.
    There is also an --enable-c++17 option to configure in case you
    want to force a build of Spot in C++17 mode.

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  Tools:

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

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

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  - genltl learned two generate two new families of formulas:
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      --fxg-or=RANGE         F(p0 | XG(p1 | XG(p2 | ... XG(pn))))
      --gxf-and=RANGE        G(p0 & XF(p1 & XF(p2 & ... XF(pn))))
    The later is a generalization of --eh-pattern=9, for which a
    single state TGBA always exists (but previous version of Spot
    would build larger automata).

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  - autfilt learned to build the union (--sum) or the intersection
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    (--sum-and) of two languages by putting two automata side-by-side
    and fiddling with the initial states.  This complements the already
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    implemented intersection (--product) and union (--product-or),
    both based on a product.
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  - autfilt learned to complement any alternating automaton with
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    option --dualize.   (See spot::dualize() below.)
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  - autfilt learned --split-edges to convert labels that are Boolean
    formulas into labels that are min-terms.  (See spot::split_edges()
    below.)

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

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

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  - The --stats=%c option of tools producing automata can now be
    restricted to count complete SCCs, using %[c]c.

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  - Tools producing automata have a --stats=... option, and tools
    producing formulas have a --format=... option.  These two options
    work similarly, the use of different names is just historical.
    Starting with this release, all tools that recognize one of these
    two options also accept the other one as an alias.

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  Library:

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  - A new library, libspotgen, gathers all functions used to generate
    families of automata or LTL formulas, used by genltl and genaut.
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  - spot::sum() and spot::sum_and() implements the union and the
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    intersection of two automata by putting them side-by-side and
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    using non-deterministim or universal branching on the initial
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    state.
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  - twa objects have a new property: prop_complete().  This obviously
    acts as a cache for the is_complete() function.

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  - spot::dualize() complements any alternating automaton.  Since
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    the dual of a deterministic automaton is still deterministic, the
    function spot::dtwa_complement() has been deprecated and simply
    calls spot::dualize().
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  - spot::decompose_strength() was extended and renamed to
    spot::decompose_scc() as it can now also extract a subautomaton
    leading to a particular SCC.  A demonstration of this feature via
    the Python bindings can be found at
    https://spot.lrde.epita.fr/ipynb/decompose.html

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  - The print_dot() function will now display names for well known
    acceptance conditions under the formula when option 'a' is used.
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    We plan to enable 'a' by default in a future release, so a new
    option 'A' has been added to hide the acceptance condition.
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  - The print_dot() function has a new experimental option 'x' to
    output labels are LaTeX formulas.  This is meant to be used in
    conjunction with the dot2tex tool.  See
      https://spot.lrde.epita.fr/oaut.html#dot2tex

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  - A new named property for automata called "original-states" can be
    used to record the origin of a state before transformation.  It is
    currently defined by the degeneralization algorithms, and by
    transform_accessible() and algorithms based on it (like
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    remove_ap::strip(), decompose_scc()).  This is realy meant as an
    aid for writing algorithms that need this mapping, but it can also
    be used to debug these algorithms: the "original-states"
    information is displayed by the dot printer when the 'd' option is
    passed.  For instance in
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      % ltl2tgba 'GF(a <-> Fb)' --dot=s
      % ltl2tgba 'GF(a <-> Fb)' | autfilt -B --dot=ds

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

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

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

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  - The new function spot::acc_cond::is_streett_like() checks whether
    an acceptance condition is conjunction of disjunctive clauses
    containing at most one Inf and at most one Fin.  It builds a
    vector of pairs to use if we want to assume the automaton has
    Streett acceptance.  The dual function is
    spot::acc_cond::is_rabin_like() works similarly.
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  - The degeneralize() function has learned to consider acceptance
    marks common to all edges comming to a state to select its initial
    level.  A similar trick was already used in sbacc(), and saves a
    few states in some cases.

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

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

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

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

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

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

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

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

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  - The function spot::streett_to_generalized_buchi() is now able to
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    work on automata with Streett-like acceptance.
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  - The function for converting deterministic Rabin automata to
    deterministic Büchi automata (when possible), internal to the
    remove_fin() procedure, has been updated to work with
    transition-based acceptance and with Rabin-like acceptance.

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  - spot::relabel_here() was used on automata to rename atomic
    propositions, it can now replace atomic propositions by Boolean
    subformula.  This makes it possible to use relabeling maps
    produced by relabel_bse() on formulas.
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  - twa_graph::copy_state_names_from() can be used to copy the state
    names from another automaton, honoring "original-states" if
    present.

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

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  - The LTL simplification routines learned that an LTL formula like
    G(a & XF(b & XFc & Fd) can be simplified to G(a & Fb & Fc & Fd),
    and dually F(a | XG(b | XGc | Gd)) = F(a | Gb | Gc | Gd).

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    When working with SERE, the simplification of "expr[*0..1]" was
    improved.  E.g. {{a[*]|b}[*0..1]} becomes {a[*]|b} instead of
    {{a[+]|b}[*0..1]}.

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

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  - spot::sbacc() is can now also convert alternating automata
    to state-based acceptance.
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  - spot::sbacc() and spot::degeneralize() learned to merge
    accepting sinks.

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

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  - The & and | operators for acceptannce conditions have been changed
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    slightly to be more symmetrical.  In older versions, operator &
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    would move Fin() terms to the front, but that is not the case
    anymore.  Also operator & was already grouping all Inf() terms
    (for efficiency reasons), in this version operator | is
    symmetrically grouping all Fin() terms.
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  - The automaton parser is now reentrant, making it possible to
    process automata from different streams at the same time (i.e.,
    using multiple spot::automaton_stream_parser instances at once).

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

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  - The parser for HOA now recognizes and verifies correct use of the
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    "univ-branch" property.  This is known to be a problem with option
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    -H1 of ltl3ba 1.1.2 and ltl3dra 0.2.4, so the environment variable
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    SPOT_HOA_TOLERANT can be set to disable the diagnostic.

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  Python:

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

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  Bugs fixed:

  - When the remove_fin() function was called on some automaton with
    Inf-less acceptance involving at least one disjunction (e.g.,
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    generalized co-Büchi), it would sometimes output an automaton with
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    transition-based acceptance but marked as state-based.

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  - The complete() function could complete an empty co-Büchi automaton
    into an automaton accepting everything.
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  Backward-incompatible changes:

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

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

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

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

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  - The color palette optionally used by print_dot() has been extended
    from 9 to 16 colors.  While the first 8 colors are similar, they
    are a bit more saturated now.

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  deprecation notices:
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  (these functions still work but compilers emit warnings.)
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  - spot::decompose_strength() is deprecated, it has been renamed
    to spot::decompose_scc().

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

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  - the spot::twa::prop_deterministic() methods have been renamed to
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    spot::twa::prop_universal() for consistency with the change to
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    is_deterministic() listed above.  we have kept
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    spot::twa::prop_deterministic() as a deprecated synonym for
    spot::twa::prop_universal() to help backward compatibility.
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  - the spot::copy() function is deprecated.  use
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    spot::make_twa_graph() instead.

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New in spot 2.3.5 (2017-06-22)
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  Bugs fixed:

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  - We have fixed new cases where translating multiple formulas in a
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    single ltl2tgba run could produce automata different from those
    produced by individual runs.
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  - The print_dot() function had a couple of issues when printing
    alternating automata: in particular, when using flag 's' (display
    SCC) or 'y' (split universal destination by colors) universal
    edges could be connected to undefined states.

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

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

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New in spot 2.3.4 (2017-05-11)
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  Bugs fixed:

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  - The transformation to state-based acceptance (spot::sbacc()) was
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    incorrect on automata where the empty acceptance mark is accepting.
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  - The --help output of randaut and ltl2tgba was showing an
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    unsupported %b stat.

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

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

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

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New in spot 2.3.3 (2017-04-11)
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  Tools:

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

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  - genltl learned --spec-patterns as an alias for --dac-patterns; it
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    also learned two new sets of LTL formulas under --hkrss-patterns
    (a.k.a. --liberouter-patterns) and --p-patterns
    (a.k.a. --beem-patterns).
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  Bugs fixed:
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  - In "lenient" mode the formula parser would fail to recover from a
    missing closing brace.
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  - The output of 'genltl --r-left=1 --r-right=1 --format=%F' had
    typos.
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  - 'ltl2tgba Fa | autfilt --complement' would incorrectly claim that
    the output is "terminal" because dtwa_complement() failed to reset
    that property.

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

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  - In bench/stutter/ the .cc files were not compiling due to warnings
    being caught as errors.
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  - The code in charge of detecting DBA-type Rabin automata is
    actually written to handle a slightly larger class of acceptance
    conditions (e.g., Fin(0)|(Fin(1)&Inf(2))), however it failed to
    correctly detect DBA-typeness in some of these non-Rabin
    acceptance.

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New in spot 2.3.2 (2017-03-15)
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  Tools:

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

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

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

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  Bugs fixed:

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

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

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

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

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

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

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

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

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

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  Deprecation notice:
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  - Using --format=%a to print the number of atomic propositions in
    ltlfilt, genltl, and randltl still works, but it is not documented
    anymore and should be replaced by the newly-introduced --format=%x
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    for consistency with tools producing automata, where %a means
    something else.
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New in spot 2.3.1 (2017-02-20)
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  Tools:

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

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

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

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

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  Library:

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

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

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  Bugs fixed:

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

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

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

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

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

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New in spot 2.3 (2017-01-19)
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  Build:

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

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

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

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

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  Tools:

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  * ltlcross supports translators that output alternating automata in
    the HOA format.  Cross-comparison checks will only work with weak
    alternating automata (not necessarily *very* weak), but "ltlcross
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    --no-check --product=0 --csv=..." will work with any alternating
    automaton if you just want satistics.
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  * autfilt can read alternating automata.  This is still experimental
    (see below). Some of the algorithms proposed by autfilt will
    refuse to work because they have not yet been updated to work with
    alternating automata, but in any case they should display a
    diagnostic: if you see a crash, please report it.

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

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  * the --check option of autfilt/ltl2tgba/ltldo/dstar2tgba can now
    take "semi-determinism" as argument.
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  * autfilt --highlight-languages will color states that recognize
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    identical languages.  (Only works for deterministic automata.)
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  * 'autfilt --sat-minimize' and 'ltl2tgba -x sat-minimize' have
    undergone some backward incompatible changes.  They use binary
    search by default, and support different options than they used
    too.  See spot-x(7) for details.  The defaults are those that were
    best for the benchmark in bench/dtgbasat/.
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  * ltlfilt learned --recurrence and --persistence to match formulas
    belonging to these two classes of the temporal hierarchy.  Unlike
    --syntactic-recurrence and --syntactic-persistence, the new checks
    are automata-based and will also match pathological formulas.
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    See https://spot.lrde.epita.fr/hierarchy.html
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  * The --format option of ltlfilt/genltl/randltl/ltlgrind learned to
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    print the class of a formula in the temporal hierarchy of Manna &
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    Pnueli using %h.  See https://spot.lrde.epita.fr/hierarchy.html
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  * ltldo and ltlcross learned a --relabel option to force the
    relabeling of atomic propositions to p0, p1, etc.  This is more
    useful with ltldo, as it allows calling a tool that restricts the
    atomic propositions it supports, and the output automaton will
    then be fixed to use the original atomic propositions.

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

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  Library:

  * A twa is required to have at least one state, the initial state.
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    An automaton can only be empty while it is being constructed,
    but should not be passed to other algorithms.
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  * Couvreur's emptiness check has been rewritten to use the explicit
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    interface when possible, to avoid overkill memory allocations.
    The new version has further optimizations for weak and terminal
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    automata.  Overall, this new version is roughly 4x faster on
    explicit automata than the former one.  The old version has been
    kept for backward compatibility, but will be removed eventually.
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  * The new version of the Couvreur emptiness check is now the default
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    one, used by twa::is_empty() and twa::accepting_run().  Always
    prefer these functions over an explicit call to Couvreur.
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  * experimental support for alternating automata:

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

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

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

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

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

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    - See https://spot.lrde.epita.fr/tut23.html
      https://spot.lrde.epita.fr/tut24.html and
      https://spot.lrde.epita.fr/tut31.html for some code examples.
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  * twa objects have two new properties, very-weak and
    semi-deterministic, that can be set or retrieved via
    twa::prop_very_weak()/twa::prop_semi_deterministic(), and that can
    be tested by is_very_weak_automaton()/is_semi_deterministic().
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  * twa::prop_set has a new attribute used in twa::prop_copy() and
    twa::prop_keep() to indicate that determinism may be improved by
    an algorithm.  In other words properties like
    deterministic/semi-deterministic/unambiguous should be preserved
    only if they are positive.

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  * language_map() and highlight_languages() are new functions that
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    implement autfilt's --highlight-languages option mentionned above.
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  * dtgba_sat_minimize_dichotomy() and dwba_sat_minimize_dichotomy()
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    use language_map() to estimate a lower bound for binary search.
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  * The encoding part of SAT-based minimization consumes less memory.
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  * SAT-based minimization of automata can now be done using two
    incremental techniques that take a solved minimization and attempt
    to forbid the use of some states.  This is done either by adding
    clauses, or by using assumptions.
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  * If the environment variable "SPOT_XCNF" is set during incremental
    SAT-based minimization, XCNF files suitable for the incremental SAT
    competition will be generated.  This requires the use of an exteral
    SAT solver, setup with "SPOT_SATSOLVER".  See spot-x(7).
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  * The new function mp_class(f) returns the class of the formula
    f in the temporal hierarchy of Manna & Pnueli.

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Python:

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

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

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

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

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

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

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New in spot 2.2.2 (2016-12-16)
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  Build:

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

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  Bug fixes:

  * scc_filter() had a left-over print statement that would print
    "names" when copying the name of the states.
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  * is_terminal() should reject automata that have accepting
    transitions going into rejecting SCCs.  The whole point of
    being a terminal automaton is that reaching an accepting
    transition guarantees that any suffix will be accepted.

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

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

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

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

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New in spot 2.2.1 (2016-11-21)
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  Bug fix:
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  * The bdd_noderesize() function, as modified in 2.2, would always
    crash.
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New in spot 2.2 (2016-11-14)
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  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).

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  * "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.

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

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

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  * is_unambiguous() was rewritten in a more efficient way.
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  * scc_info learned to determine the acceptance of simple SCCs made
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    of a single self-loop without resorting to remove_fin() for complex
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    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.
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  * Simulation-based reductions now implement just bisimulation-based
    reductions on deterministic automata, to save time.  As an example,
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    this halves the run time of
       genltl --rv-counter=10 | ltl2tgba

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

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

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  * The twa class has three new methods:
      aut->intersects(other)
      aut->intersecting_run(other)
      aut->intersecting_word(other)
    currently these are just convenient wrappers around
      !otf_product(aut, other)->is_empty()
      otf_product(aut, other)->accepting_run()->project(aut)
      otf_product(aut, other)->accepting_word()
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    with any Fin-acceptance removal performed before the product.
    However the plan is to implement these more efficiently in the
    future.
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  Bug fixes:
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  * ltl2tgba was always using the highest settings for the LTL
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    simplifier, ignoring the --low and --medium options.  Now
      genltl --go-theta=12 | ltl2tgba --low --any
    is instantaneous as it should be.

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  * The int-vector compression code could encode 6 and 22 in the
    same way, causing inevitable issues in our LTSmin interface.
    (This affects tests/ltsmin/modelcheck with option -z, not -Z.)
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  * str_sere() and str_utf8_sere() were not returning the same
    string that print_sere() and print_utf8_sere() would print.

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  * Running the LTL parser in debug mode would crash.
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  * tgba_determinize() could produce incorrect deterministic automata
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    when run with use_simulation=true (the default) on non-simplified
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    automata.

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

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  * calling set_acceptance() several times on an automaton could
    result in unexpected behaviors, because set_acceptance(0,...)
    used to set the state-based acceptance flag automatically.
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  * Some buffering issue caused syntax errors to be displayed out
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    of place by the on-line translator.
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  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.

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  * 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.

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  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)).

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  Bug fixes:

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  * Fix spurious uninitialized read reported by valgrind when
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    is_Kleene_star() is compiled by clang++.
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  * Using "ltlfilt some-large-file --some-costly-filter" could take
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    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.

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

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

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New in spot 2.1.1 (2016-09-20)
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  Command-line tools:

  * ltlfilt, randltl, genltl, and ltlgrind learned to display the size
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    (%s), Boolean size (%b), and number of atomic propositions (%a)
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    with the --format and --output options.  A typical use-case is to
    sort formulas by size:
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       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'

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

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

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  Bugs fixed:

  * Fix several cases where command-line tools would fail to diagnose
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    write errors (e.g. when writing to a filesystem that is full).
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  * Typos in genltl --help and in the man page spot-x(7).
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New in spot 2.1 (2016-08-08)
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  Command-line tools:

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  * 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.

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

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  * ltlcross and ltldo learned to bypass the shell when executing
    simple commands (with support for single or double-quoted
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    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.
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  * autfilt learned to filter automata by count of SCCs (--sccs=RANGE)
    or by type of SCCs (--accepting-sccs=RANGE,
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    --rejecting-sccs=RANGE, trivial-sccs=RANGE, --terminal-sccs=RANGE,
    --weak-sccs=RANGE, --inherently-weak-sccs=RANGE).

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

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  * autfilt learned to filter automata by count of nondeterministsic
    states with --nondet-states=RANGE.
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  * autfilt learned to filter automata representing stutter-invariant
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    properties with --is-stutter-invariant.

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  * autfilt learned two new options to highlight non-determinism:
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    --highlight-nondet-states=NUM and --highlight-nondet-states=NUM
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    where NUM is a color number.  Additionally --highlight-nondet=NUM is
    a shorthand for using the two.
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  * autfilt learned to highlight a run matching a given word using the
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    --highlight-word=[NUM,]WORD option.  However currently this only
    work on automata with Fin-less acceptance.

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

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  * genltl learned three new families: --dac-patterns=1..45,
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    --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 &
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    Holzmann (Concur'00), Somenzi & Bloem (CAV'00).
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  * genltl learned two options, --positive and --negative, to control
    wether formulas should be output after negation or not (or both).
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  * 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.

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  * The --stats option of autfilt, dstar2tgba, ltl2tgba, ltldo,
    randaut learned to display the output (or input if that makes