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mini_ic3: fix generalize() returning empty/init-overlapping core (#9245)

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Two fixes in examples/python/mini_ic3.py:

1. generalize(): the polarity of the disjointness check was inverted,
   and there was no guard against an empty unsat core. With an empty
   core, And([])=True so check_disjoint(init, prev(True)) is always
   False (init is sat), and the code returned the empty core. That
   empty core then became cube2clause([])=Or([])=False, which got
   added as a lemma to all frames. The frame became inconsistent and
   is_valid() returned And(Or())=False as the "inductive invariant".

   Fix: require len(core) > 0 AND check_disjoint(init, prev(core))
   (without the spurious 'not'), so the core is only used when it
   is genuinely disjoint from init.

2. is_transition(): when an init rule's body happens to be an And
   without any Invariant predicate (e.g. (and (not A) (not B) ...)),
   is_body() returns (And(...), None). is_transition then passed
   inv0=None to subst_vars() which crashed inside get_vars(). Add an
   explicit None check so the rule falls through to is_init().

Verified on horn1..5 (unchanged behavior), h_CRC and h_FIFO from the
blocksys benchmarks (now correctly return CEX matching z3 spacer),
and cache_coherence_three (no longer collapses to (and or)).
This commit is contained in:
Guangyu (Gary) HU 2026-04-09 17:01:07 +08:00 • committed by GitHub
parent 5d0141d916
commit 704dc9375d
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1 changed files with 3 additions and 1 deletions
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examples/python/mini_ic3.py
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@ -74,6 +74,8 @@ class Horn2Transitions:
pred, inv0 = self.is_body(body)
if pred is None:
return False
if inv0 is None:
return False
inv1 = self.is_inv(head)
if inv1 is None:
return False
@ -335,7 +337,7 @@ class MiniIC3:
s = self.states[f - 1].solver
if unsat == s.check(cube):
core = s.unsat_core()
if not check_disjoint(self.init, self.prev(And(core))):
if len(core) > 0 and check_disjoint(self.init, self.prev(And(core))):
return core, f
return cube, f