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BDD: add AF AG dead-end reproducer #2002

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BDD: add AF AG dead-end reproducer #2002

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14 changes: 14 additions & 0 deletions regression/ebmc/BDD/AFAG_deadend1.desc
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KNOWNBUG
AFAG_deadend1.smv
--bdd
^\[spec1\] AF AG good: PROVED$
^EXIT=0$
^SIGNAL=0$
--
^warning: ignoring
--
The BDD implementation of nested AG uses AG p = !EF !p over the raw
transition relation. A finite branch into a deadend state with !p is therefore
treated as a witness against AG p, even though the existing deadend regressions
use conventions where finite deadend branches do not falsify universal
properties.
12 changes: 12 additions & 0 deletions regression/ebmc/BDD/AFAG_deadend1.smv
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MODULE main

VAR good : boolean;

INIT good = TRUE

TRANS good & next(good) | good & !next(good)

-- There is an infinite path that stays in good forever and a finite path to a
-- deadend state with good = FALSE. Under the deadend conventions used by the
-- existing BDD regressions, the finite branch should not falsify AG good.
SPEC AF AG good