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+/*********************                                                        */
+/*! \file candidate.h
+ ** \verbatim
+ ** Top contributors (to current version):
+ **   Gereon Kremer
+ ** 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 Represents a contraction candidate for ICP-style propagation.
+ **/
+
+#ifndef CVC4__THEORY__ARITH__ICP__CANDIDATE_H
+#define CVC4__THEORY__ARITH__ICP__CANDIDATE_H
+
+#include "util/real_algebraic_number.h"
+
+#ifdef CVC4_POLY_IMP
+#include <poly/polyxx.h>
+
+#include "expr/node.h"
+#include "theory/arith/nl/icp/intersection.h"
+
+namespace CVC4 {
+namespace theory {
+namespace arith {
+namespace nl {
+namespace icp {
+
+/**
+ * A contraction candidate for ICP-style propagation with the following
+ * semantics:
+ *
+ *   lhs  ~rel~  rhsmult*rhs
+ *
+ * where lhs is the variable whose interval we aim to contract, rel is a
+ * relation symbol (other than disequality), rhsmult is a fractional constant
+ * and rhs a polynomial. As poly::Polynomial only holds integer polynomials,
+ * rhsmult is necessary to encode polynomials with rational coefficients.
+ *
+ * Additionally, we store the origin of this constraints (a single theory
+ * constraint) and the variables contained in rhs.
+ *
+ * A candidate is evaluated (or propagated) by evaluating the rhsmult*rhs over
+ * an interval assignment and then updating the interval assignment for lhs with
+ * the result of this evaluation, properly considering the relation.
+ */
+struct Candidate
+{
+  /** The target variable */
+  poly::Variable lhs;
+  /** The relation symbol */
+  poly::SignCondition rel;
+  /** The (integer) polynomial on the right hand side */
+  poly::Polynomial rhs;
+  /** The rational multiplier */
+  poly::Rational rhsmult;
+  /** The origin of this candidate */
+  Node origin;
+  /** The variable within rhs */
+  std::vector<Node> rhsVariables;
+
+  /**
+   * Contract the interval assignment based on this candidate.
+   * Only contract if the new interval is below the given threshold, see
+   * intersect_interval_with().
+   */
+  PropagationResult propagate(poly::IntervalAssignment& ia,
+                              std::size_t size_threshold) const;
+};
+
+/** Print a candidate. */
+std::ostream& operator<<(std::ostream& os, const Candidate& c);
+
+}  // namespace icp
+}  // namespace nl
+}  // namespace arith
+}  // namespace theory
+}  // namespace CVC4
+
+#endif
+
+#endif