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/********************* */
/*! \file sygus_abduct.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 Sygus abduction preprocessing pass, which transforms an arbitrary
** input into an abduction problem.
**/
#ifndef CVC4__PREPROCESSING__PASSES__SYGUS_ABDUCT_H
#define CVC4__PREPROCESSING__PASSES__SYGUS_ABDUCT_H
#include "preprocessing/preprocessing_pass.h"
#include "preprocessing/preprocessing_pass_context.h"
namespace CVC4 {
namespace preprocessing {
namespace passes {
/** SygusAbduct
*
* A preprocessing utility that turns a set of quantifier-free assertions into
* a sygus conjecture that encodes an abduction problem. In detail, if our
* input formula is F( x ) for free symbols x, then we construct the sygus
* conjecture:
*
* exists A. forall x. ( A( x ) => ~F( x ) )
*
* where A( x ) is a predicate over the free symbols of our input. In other
* words, A( x ) is a sufficient condition for showing ~F( x ).
*
* Another way to view this is A( x ) is any condition such that A( x ) ^ F( x )
* is unsatisfiable.
*
* A common use case is to find the weakest such A that meets the above
* specification. We do this by streaming solutions (sygus-stream) for A
* while filtering stronger solutions (sygus-filter-sol=strong). These options
* are enabled by default when this preprocessing class is used (sygus-abduct).
*
* If the input F( x ) is partitioned into axioms Fa and negated conjecture Fc
* Fa( x ) ^ Fc( x ), then the sygus conjecture we construct is:
*
* exists A. ( exists y. A( y ) ^ Fa( y ) ) ^ forall x. ( A( x ) => ~F( x ) )
*
* In other words, A( y ) must be consistent with our axioms Fa and imply
* ~F( x ). We encode this conjecture using SygusSideConditionAttribute.
*/
class SygusAbduct : public PreprocessingPass
{
public:
SygusAbduct(PreprocessingPassContext* preprocContext);
/**
* Returns the sygus conjecture corresponding to the abduction problem for
* input problem (F above) given by asserts, and axioms (Fa above) given by
* axioms. Note that axioms is expected to be a subset of asserts.
*
* The type abdGType (if non-null) is a sygus datatype type that encodes the
* grammar that should be used for solutions of the abduction conjecture.
*/
static Node mkAbductionConjecture(const std::vector<Node>& asserts,
const std::vector<Node>& axioms,
TypeNode abdGType);
protected:
/**
* Replaces the set of assertions by an abduction sygus problem described
* above.
*/
PreprocessingPassResult applyInternal(
AssertionPipeline* assertionsToPreprocess) override;
};
} // namespace passes
} // namespace preprocessing
} // namespace CVC4
#endif /* CVC4__PREPROCESSING__PASSES__SYGUS_ABDUCT_H_ */
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