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+/******************************************************************************
+ * Top contributors (to current version):
+ *   Andrew Reynolds, Gereon Kremer
+ *
+ * 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.
+ * ****************************************************************************
+ *
+ * The abstract proof generator class.
+ */
+
+#include "cvc5_private.h"
+
+#ifndef CVC5__PROOF__PROOF_GENERATOR_H
+#define CVC5__PROOF__PROOF_GENERATOR_H
+
+#include "expr/node.h"
+
+namespace cvc5 {
+
+class CDProof;
+class ProofNode;
+
+/** An overwrite policy for CDProof */
+enum class CDPOverwrite : uint32_t
+{
+  // always overwrite an existing step.
+  ALWAYS,
+  // overwrite ASSUME with non-ASSUME steps.
+  ASSUME_ONLY,
+  // never overwrite an existing step.
+  NEVER,
+};
+/** Writes a overwrite policy name to a stream. */
+std::ostream& operator<<(std::ostream& out, CDPOverwrite opol);
+
+/**
+ * An abstract proof generator class.
+ *
+ * A proof generator is intended to be used as a utility e.g. in theory
+ * solvers for constructing and storing proofs internally. A theory may have
+ * multiple instances of ProofGenerator objects, e.g. if it has more than one
+ * way of justifying lemmas or conflicts.
+ *
+ * A proof generator has two main interfaces for generating proofs:
+ * (1) getProofFor, and (2) addProofTo. The latter is optional.
+ *
+ * The addProofTo method can be used as an optimization for avoiding
+ * the construction of the ProofNode for a given fact.
+ *
+ * If no implementation of addProofTo is provided, then addProofTo(f, pf)
+ * calls getProofFor(f) and links the topmost ProofNode of the returned proof
+ * into pf. Note this top-most ProofNode can be avoided in the addProofTo
+ * method.
+ */
+class ProofGenerator
+{
+ public:
+  ProofGenerator();
+  virtual ~ProofGenerator();
+  /** Get the proof for formula f
+   *
+   * This forces the proof generator to construct a proof for formula f and
+   * return it. If this is an "eager" proof generator, this function is expected
+   * to be implemented as a map lookup. If this is a "lazy" proof generator,
+   * this function is expected to invoke a proof producing procedure of the
+   * generator.
+   *
+   * It should be the case that hasProofFor(f) is true.
+   *
+   * @param f The fact to get the proof for.
+   * @return The proof for f.
+   */
+  virtual std::shared_ptr<ProofNode> getProofFor(Node f);
+  /**
+   * Add the proof for formula f to proof pf. The proof of f is overwritten in
+   * pf based on the policy opolicy.
+   *
+   * @param f The fact to get the proof for.
+   * @param pf The CDProof object to add the proof to.
+   * @param opolicy The overwrite policy for adding to pf.
+   * @param doCopy Whether to do a deep copy of the proof steps into pf.
+   * @return True if this call was sucessful.
+   */
+  virtual bool addProofTo(Node f,
+                          CDProof* pf,
+                          CDPOverwrite opolicy = CDPOverwrite::ASSUME_ONLY,
+                          bool doCopy = false);
+  /**
+   * Can we give the proof for formula f? This is used for debugging. This
+   * returns false if the generator cannot provide a proof of formula f.
+   *
+   * Also notice that this function does not require the proof for f to be
+   * constructed at the time of this call. Thus, if this is a "lazy" proof
+   * generator, it is expected that this call is implemented as a map lookup
+   * into the bookkeeping maintained by the generator only.
+   *
+   * Notice the default return value is true. In other words, a proof generator
+   * may choose to override this function to verify the construction, although
+   * we do not insist this is the case.
+   */
+  virtual bool hasProofFor(Node f) { return true; }
+  /** Identify this generator (for debugging, etc..) */
+  virtual std::string identify() const = 0;
+};
+
+}  // namespace cvc5
+
+#endif /* CVC5__PROOF__PROOF_GENERATOR_H */