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tl: add some implication-based rewritings for "<->", "->", and "xor"

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This prevents an exception from being raised if NNF is not performed
on Boolean properties and implication-based checks are used.

* NEWS: Mention the issue.
* spot/tl/simplify.cc, doc/tl/tl.tex: Add some rules.
* tests/python/ltlsimple.py: Test them.
This commit is contained in:
Alexandre Duret-Lutz 2018-08-01 15:00:45 +02:00
parent d8419db618
commit 126d392355
4 changed files with 113 additions and 58 deletions
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34
spot/tl/simplify.cc
View file

@ -1775,12 +1775,38 @@ namespace spot
trace << "bo: trying inclusion-based rules" << std::endl;
switch (o)
{
case op::Xor:
case op::Equiv:
{
if (c_->implication(a, b))
return recurse(formula::Implies(b, a));
if (c_->implication(b, a))
return recurse(formula::Implies(a, b));
break;
}
case op::Implies:
SPOT_UNIMPLEMENTED();
break;
{
if (c_->implication(a, b))
return formula::tt();
break;
}
case op::Xor:
{
// if (!a)->b then a xor b = b->!a = a->!b
if (c_->implication_neg(a, b, false))
{
if (b.is(op::Not))
return recurse(formula::Implies(a, b[0]));
return recurse(formula::Implies(b, formula::Not(a)));
}
// if a->!b then a xor b = (!b)->a = (!a)->b
if (c_->implication_neg(a, b, true))
{
if (b.is(op::Not))
return recurse(formula::Implies(b[0], a));
return recurse(formula::Implies(formula::Not(a), b));
}
break;
}
case op::U:
// if a => b, then a U b = b
if (c_->implication(a, b))