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/********************* */
/*! \file skolem_cache.cpp
** \verbatim
** Top contributors (to current version):
** Andrew Reynolds, Morgan Deters
** This file is part of the CVC4 project.
** Copyright (c) 2009-2020 by the authors listed in the file AUTHORS
** in the top-level source directory and their institutional affiliations.
** All rights reserved. See the file COPYING in the top-level source
** directory for licensing information.\endverbatim
**
** \brief Arrays skolem cache
**/
#include "theory/arrays/skolem_cache.h"
#include "expr/attribute.h"
#include "expr/bound_var_manager.h"
#include "expr/skolem_manager.h"
#include "expr/type_node.h"
using namespace CVC4::kind;
namespace CVC4 {
namespace theory {
namespace arrays {
/**
* A bound variable corresponding to an index for witnessing the satisfiability
* of array disequalities.
*/
struct ExtIndexVarAttributeId
{
};
typedef expr::Attribute<ExtIndexVarAttributeId, Node> ExtIndexVarAttribute;
SkolemCache::SkolemCache() {}
Node SkolemCache::getExtIndexSkolem(Node deq)
{
Assert(deq.getKind() == NOT && deq[0].getKind() == EQUAL);
Node a = deq[0][0];
Node b = deq[0][1];
Assert(a.getType().isArray());
Assert(b.getType() == a.getType());
NodeManager* nm = NodeManager::currentNM();
// get the reference index, which notice is deterministic for a, b in the
// lifetime of the node manager
Node x = getExtIndexVar(deq);
// make the axiom for x
Node as = nm->mkNode(SELECT, a, x);
Node bs = nm->mkNode(SELECT, b, x);
Node deqIndex = as.eqNode(bs).notNode();
Node axiom = nm->mkNode(IMPLIES, deq, deqIndex);
// make the skolem that witnesses the above axiom
SkolemManager* sm = nm->getSkolemManager();
return sm->mkSkolem(
x,
axiom,
"array_ext_index",
"an extensional lemma index variable from the theory of arrays");
}
Node SkolemCache::getExtIndexVar(Node deq)
{
Node a = deq[0][0];
TypeNode atn = a.getType();
Assert(atn.isArray());
Assert(atn == deq[0][1].getType());
TypeNode atnIndex = atn.getArrayIndexType();
BoundVarManager* bvm = NodeManager::currentNM()->getBoundVarManager();
return bvm->mkBoundVar<ExtIndexVarAttribute>(deq, atnIndex);
}
} // namespace arrays
} // namespace theory
} // namespace CVC4
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