Preprocessing extensions - #886
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Implements the technique of Khasidashvili and Korovin (SAT 2016): a predicate P
occurring at most once in every clause is eliminated by replacing S_P and S_~P
with all pairwise resolvents on P. On problems without equality and theories,
resolvents are computed with an mgu and non-unifiable pairs dropped; otherwise
the P-literals are (virtually) flattened, introducing argument disequalities
which are then simplified away by exhaustive equality substitution (this can
introduce equality into a problem previously without it). FMB forces the
equational mode, since its model reconstruction cannot rely on the
Herbrand-interpretation argument justifying the mgu variant.
Elimination steps are gated SAT-VE-style by growth limits on the estimated
clause count |S_P|*|S_~P| - |S_P| - |S_~P|: a per-step tolerance factor over
the current total (-pelst, default 1.05) and a global cap relative to the
original total (-peltl, default 2.0). Syntactic tautologies (complementary
pair, t != t, s = s) and duplicate literals are removed from generated
resolvents, and the actual surviving count feeds back into the budget.
The next predicate to eliminate is by default the one with the smallest
estimated growth (pure predicates thus go first, their clauses being simply
deleted); with -pelr the choice is uniformly random among the admissible
candidates (controlled by random_seed), since the process is not confluent.
With -pels, the clause set is kept forward-inter-subsumed throughout, using a
standalone LiteralSubstitutionTree index (unit literal, or the least matchable
one) plus SATSubsumptionAndResolution; backward subsumption is left as future
work.
Every elimination records a model-repairing definition
P(xs) <=> \/_{D \/ P(ts) in S_P} exists ys. (xs = ts /\ ~D)
via Problem::addEliminatedPredicate (addTrivialPredicate for pure ones), so
both the textual model updates output and FMB model restoration stay correct
(verified via --mode model_check).
Skipped for higher-order/polymorphic inputs (predicates could hide inside
terms, breaking the occurrence counting) and for color-annotated problems.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Pushes quantifiers inside rectified/NNF/flattened formulas just before Skolemization (old clausification pipeline only; no effect with newcnf), so Skolem functions get fewer arguments. Duplicated binders are renamed on the fly to keep formulas rectified, as Skolemization requires. Skipped for higher-order and polymorphic problems: SubstHelper cannot rename under lambdas, and FormulaVarIterator does not see type variables inside binder sorts. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
… log-uniformly from [nm/2, 2*nm] Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
…ndividual definition eliminations Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
…a candidate inequality (a pass with all candidates skipped ends the per-clause fixpoint) Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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…ered blocking (the dropped candidate is never re-enqueued, so the clause can only still get blocked via one of its other literals) Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
…andidate predicate (marking it never-to-be-reconsidered, so it stays in the problem for good) Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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For now adding miniscoping, to be experimented with