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/******************************************************************************
* Top contributors (to current version):
* Andrew Reynolds, Mathias Preiner, Paul Meng
*
* This file is part of the cvc5 project.
*
* Copyright (c) 2009-2021 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.
* ****************************************************************************
*
* Alpha equivalence checking.
*/
#include "cvc5_private.h"
#ifndef CVC5__ALPHA_EQUIVALENCE_H
#define CVC5__ALPHA_EQUIVALENCE_H
#include "theory/quantifiers/quant_util.h"
#include "expr/term_canonize.h"
namespace cvc5 {
namespace theory {
namespace quantifiers {
/**
* This trie stores a trie of the above form for each multi-set of types. For
* each term t registered to this node, we store t in the appropriate
* AlphaEquivalenceNode trie. For example, if t contains 2 free variables
* of type T1 and 3 free variables of type T2, then it is stored at
* d_children[T1][2].d_children[T2][3].
*/
class AlphaEquivalenceTypeNode {
public:
/** children of this node */
std::map<std::pair<TypeNode, size_t>, AlphaEquivalenceTypeNode> d_children;
/**
* map from canonized quantifier bodies to a quantified formula whose
* canonized body is that term.
*/
std::map<Node, Node> d_quant;
/** register node
*
* This registers term q to this trie. The term t is the canonical form of
* q, typs/typCount represent a multi-set of types of free variables in t.
*/
Node registerNode(Node q,
Node t,
std::vector<TypeNode>& typs,
std::map<TypeNode, size_t>& typCount);
};
/**
* Stores a database of quantified formulas, which computes alpha-equivalence.
*/
class AlphaEquivalenceDb
{
public:
AlphaEquivalenceDb(expr::TermCanonize* tc) : d_tc(tc) {}
/** adds quantified formula q to this database
*
* This function returns a quantified formula q' that is alpha-equivalent to
* q. If q' != q, then q' was previously added to this database via a call
* to addTerm.
*/
Node addTerm(Node q);
private:
/** a trie per # of variables per type */
AlphaEquivalenceTypeNode d_ae_typ_trie;
/** pointer to the term canonize utility */
expr::TermCanonize* d_tc;
};
/**
* A quantifiers module that computes reductions based on alpha-equivalence,
* using the above utilities.
*/
class AlphaEquivalence
{
public:
AlphaEquivalence();
~AlphaEquivalence(){}
/** reduce quantifier
*
* If non-null, its return value is lemma justifying why q is reducible.
* This is of the form ( q = q' ) where q' is a quantified formula that
* was previously registered to this class via a call to reduceQuantifier,
* and q and q' are alpha-equivalent.
*/
Node reduceQuantifier( Node q );
private:
/** a term canonizer */
expr::TermCanonize d_termCanon;
/** the database of quantified formulas registered to this class */
AlphaEquivalenceDb d_aedb;
};
}
}
} // namespace cvc5
#endif
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