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/********************* */
/*! \file ackermann.h
** \verbatim
** Top contributors (to current version):
** Aina Niemetz, Yoni Zohar
** 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 Ackermannization preprocessing pass.
**
** This implements the Ackermannization preprocessing pass, which enables
** very limited theory combination support for eager bit-blasting via
** Ackermannization. It reduces constraints over the combination of the
** theories of fixed-size bit-vectors and uninterpreted functions as
** described in
** Liana Hadarean, An Efficient and Trustworthy Theory Solver for
** Bit-vectors in Satisfiability Modulo Theories.
** https://cs.nyu.edu/media/publications/hadarean_liana.pdf
**/
#include "cvc4_private.h"
#ifndef CVC4__PREPROCESSING__PASSES__ACKERMANN_H
#define CVC4__PREPROCESSING__PASSES__ACKERMANN_H
#include <unordered_map>
#include "expr/node.h"
#include "preprocessing/preprocessing_pass.h"
#include "preprocessing/preprocessing_pass_context.h"
namespace CVC4 {
namespace preprocessing {
namespace passes {
using TNodeSet = std::unordered_set<TNode, TNodeHashFunction>;
using FunctionToArgsMap =
std::unordered_map<TNode, TNodeSet, TNodeHashFunction>;
class Ackermann : public PreprocessingPass
{
public:
Ackermann(PreprocessingPassContext* preprocContext);
protected:
/**
* Apply Ackermannization as follows:
*
* - For each application f(X) where X = (x1, . . . , xn), introduce a fresh
* variable f_X and use it to replace all occurrences of f(X).
*
* - For each f(X) and f(Y) with X = (x1, . . . , xn) and Y = (y1, . . . , yn)
* occurring in the input formula, add the following lemma:
* (x_1 = y_1 /\ ... /\ x_n = y_n) => f_X = f_Y
*/
PreprocessingPassResult applyInternal(
AssertionPipeline* assertionsToPreprocess) override;
private:
/* Map each function to a set of terms associated with it */
FunctionToArgsMap d_funcToArgs;
/* Map each function term to the new Skolem variable created by
* ackermannization */
theory::SubstitutionMap d_funcToSkolem;
};
} // namespace passes
} // namespace preprocessing
} // namespace CVC4
#endif /* CVC4__PREPROCESSING__PASSES__ACKERMANN_H */
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