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/********************* */
/*! \file subs_minimize.h
** \verbatim
** Top contributors (to current version):
** Andrew Reynolds
** This file is part of the CVC4 project.
** Copyright (c) 2009-2019 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 Substitution minimization.
**/
#include "cvc4_private.h"
#ifndef __CVC4__THEORY__SUBS_MINIMIZE_H
#define __CVC4__THEORY__SUBS_MINIMIZE_H
#include <vector>
#include "expr/node.h"
namespace CVC4 {
namespace theory {
/** SubstitutionMinimize
*
* This class is used for finding a minimal substitution under which an
* evaluation holds.
*/
class SubstitutionMinimize
{
public:
SubstitutionMinimize();
~SubstitutionMinimize() {}
/** find
*
* If t { vars -> subs } rewrites to target, this method returns true, and
* vars[i_1], ..., vars[i_n] are added to reqVars, such that i_1, ..., i_n are
* distinct, and t { vars[i_1] -> subs[i_1], ..., vars[i_n] -> subs[i_n] }
* rewrites to target.
*
* If t { vars -> subs } does not rewrite to target, this method returns
* false.
*/
static bool find(Node t,
Node target,
const std::vector<Node>& vars,
const std::vector<Node>& subs,
std::vector<Node>& reqVars);
/** find with implied
*
* This method should be called on a formula t.
*
* If t { vars -> subs } rewrites to true, this method returns true,
* vars[i_1], ..., vars[i_n] are added to reqVars, and
* vars[i_{n+1}], ..., vars[i_{n+m}] are added to impliedVars such that
* i_1...i_{n+m} are distinct, i_{n+1} < ... < i_{n+m}, and:
*
* (1) t { vars[i_1]->subs[i_1], ..., vars[i_{n+k}]->subs[i_{n+k}] } implies
* vars[i_{n+k+1}] = subs[i_{n+k+1}] for k = 0, ..., m-1.
*
* (2) t { vars[i_1] -> subs[i_1], ..., vars[i_{n+m}] -> subs[i_{n+m}] }
* rewrites to true.
*
* For example, given (x>0 ^ x = y ^ y = z){ x -> 1, y -> 1, z -> 1, w -> 0 },
* this method may add { x } to reqVars, and { y, z } to impliedVars.
*
* Notice that the order of variables in vars matters. By the semantics above,
* variables that appear earlier in the variable list vars are more likely
* to appear in reqVars, whereas those later in the vars are more likely to
* appear in impliedVars.
*/
static bool findWithImplied(Node t,
const std::vector<Node>& vars,
const std::vector<Node>& subs,
std::vector<Node>& reqVars,
std::vector<Node>& impliedVars);
private:
/** Common helper function for the above functions. */
static bool findInternal(Node t,
Node target,
const std::vector<Node>& vars,
const std::vector<Node>& subs,
std::vector<Node>& reqVars);
/** is singular arg
*
* Returns true if
* <k>( ... t_{arg-1}, n, t_{arg+1}...) = c
* always holds for some constant c.
*/
static bool isSingularArg(Node n, Kind k, unsigned arg);
};
} // namespace theory
} // namespace CVC4
#endif /* __CVC4__THEORY__SUBS_MINIMIZE_H */
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