We are happy to announce the release of Spot 2.9 Spot is a library of algorithms for manipulating LTL formulas and omega-automata. This is a major release that has been under development for 9 months. It contains new features contributed by from Florian Renkin and myself. A summary of those changes is given at the end of this email. Note that version 2.9 and the following 2.9.x minor releases are likely to be the last releases using C++14. We plan is to switch to C++17 for the next major release. The current code-base is already compatible with C++17, so tools using Spot as a library may consider switching to C++17 already. You can find the new release here: http://www.lrde.epita.fr/dload/spot/spot-2.9.tar.gz See https://spot.lrde.epita.fr/ for documentation and installation instructions. Please direct any feedback to <spot@lrde.epita.fr>. New in spot 2.9 (2020-04-30) Command-line tools: - When the --check=stutter-sensitive-example option is passed to tools like ltl2tgba, autfilt, genaut, or ltldo, the produced automata are checked for stutter-invariance (as in the --check=stutter-invariant case), additionally a proof of stutter-sensitiveness is provided as two stutter-equivalent words: one accepted, and one rejected. These sample words are printed in the HOA output. % ltl2tgba --check=stutter-sensitive-example Xa | grep word: spot-accepted-word: "!a; cycle{a}" spot-rejected-word: "!a; !a; cycle{a}" - autfilt learned the --partial-degeneralize option, to remove conjunctions of Inf, or disjunctions of Fin that appears in arbitrary conditions. - ltlfilt and autfilt learned a --nth=RANGE (a.k.a. -N) option to select a range of their input formulas or automata (assuming a 1-based numbering). - When running translators, ltlcross will now display {names} when supplied. - ltlcross is now using the generic emptiness check procedure introduced in Spot 2.7, as opposed to removing Fin acceptance before using a classical emptiness check. - ltlcross learned a --save-inclusion-products=FILENAME option. Its use cases are probably quite limited. We use that to generate benchmarks for our generic emptiness check procedure. - ltlsynt --algo=lar uses the new version of to_parity() mentionned below. The old version is available via --algo=lar.old - ltlsynt learned --csv=FILENAME, to record some statistics about the duration of its different phases. - The dot printer is now automatically using rectangles with rounded corners for automata states if one state label have five or more characters. This saves space with very long labels. Use --dot=c, --dot=e, or --dot=E to force the use of Circles, Ellipses, or rEctangles. Library: - Historically, Spot only supports LTL with infinite semantics so it had automatic simplifications reducing X(1) and X(0) to 1 and 0 whenever such formulas are constructed. This caused issues for users of LTLf formulas, where it is important to distinguish a "weak next" (for which X(1)=1 but X(0)!=0) from a "strong next" (for which X(0)=0 but X(1)!=1). To accommodate this, this version introduces a new operator op::strong_X in addition to the existing op::X (whose interpretation is now weak in LTLf). The syntax for the strong next is X[!] as a reference to the PSL syntax (where the strong next is written X!). Trivial simplification rules for X are changed to just X(1) = 1 (and not X(0)=0 anymore) while we have X[!]0 = 0 The X(0)=0 and X[!]1=1 reductions are now preformed during LTL simplification, not automatically. Aside from the from_ltlf() function, the other functions of the library handle X and X[!] in the same way, since there is no difference between X and X[!] over infinite words. Operators F[n:m!] and G[n:m!] are also supported as strong variants of F[n:m] and G[n:m], but those four are only implemented as syntactic sugar. - acc_cond::acc_code::parity(bool, bool, int) was not very readable, as it was unclear to the reader what the boolean argument meant. The following sister functions can now improve readability: parity_max(is_odd, n) = parity(true, is_odd, n) parity_max_odd(n) = parity_max(true, n) parity_max_even(n) = parity_max(false, n) parity_min(is_odd, n) = parity(false, is_odd, n) parity_min_odd(n) = parity_min(true, n) parity_min_even(n) = parity_min(false, n) - partial_degeneralize() is a new function performing partial degeneralization to get rid of conjunctions of Inf terms, or disjunctions of Fin terms in acceptance conditions. - simplify_acceptance_here() and simplify_acceptance() learned to simplify subformulas like Fin(i)&Fin(j) or Inf(i)|Inf(j), or some more complex variants of those. If i is uniquely used in the acceptance condition, these become respectively Fin(i) or Inf(i), and the automaton is adjusted so that i also appears where j appeared. - acc_code::unit_propagation() is a new method for performing unit propagation in acceptance condition. E.g. Fin(0) | (Inf(0) & Inf(1)) becomes Fin(0) | Inf(1). This is now called by simplify_acceptance_here(). - propagate_marks_vector() and propagate_marks_here() are helper functions for propagating marks on the automaton: ignoring self-loops and out-of-SCC transitions, marks common to all the input transitions of a state can be pushed to all its outgoing transitions, and vice-versa. This is repeated until a fix point is reached. propagate_marks_vector() does not modify the automaton and returns a vector of the acc_cond::mark_t that should be on each transition; propagate_marks_here() actually modifies the automaton. - rabin_to_buchi_if_realizable() is a new variant of rabin_to_buchi_maybe() that converts a Rabin-like automaton into a Büchi automaton only if the resulting Büchi automaton can keep the same transition structure (where the ..._maybe() variant would modify the Rabin automaton if needed). - to_parity() has been rewritten. It now combines several strategies for paritizing automata with any acceptance condition. - relabel_bse(), used by ltlfilt --relabel-bool, is now better at dealing with n-ary operators and isolating subsets of operands that can be relabeled as a single term. - print_dot()'s default was changed to use circles for automata with fewer than 10 unamed states, ellipses for automata with up to 1000 unamed states (or named states with up to 4 characters), and rounded rectangles otherwise. Rectangles are also used for automata with acceptance bullets on states. The new "E" option can be used to force rectangles in all situations. - The generic emptiness check has been slightly improved (doing fewer recursive calls in the worst case). Backward-incompatible changes: - iar() and iar_maybe() have been moved from spot/twaalgos/rabin2parity.hh spot/twaalgos/toparity.hh and marked as deprecated, they should be replaced by to_parity(). In case the input is Rabin-like or Streett-like, to_parity() should be at least as good as iar(). - The twa_graph::is_alternating() and digraph::is_alternating() methods, deprecated in Spot 2.3.1 (2017-02-20), have been removed. Bugs fixed: - Relabeling automata could introduce false edges. Those are now removed. - Emptiness checks, and scc_info should now ignore edges labeled with false. - relabel_bse() could incorrectly relabel Boolean subformulas that had some atomic propositions in common. -- Alexandre Duret-Lutz