src/theory/trust_node.h

   1 /*********************                                                        */
   2 /*! \file trust_node.h
   3  ** \verbatim
   4  ** Top contributors (to current version):
   5  **   Andrew Reynolds
   6  ** This file is part of the CVC4 project.
   7  ** Copyright (c) 2009-2020 by the authors listed in the file AUTHORS
   8  ** in the top-level source directory) and their institutional affiliations.
   9  ** All rights reserved.  See the file COPYING in the top-level source
  10  ** directory for licensing information.\endverbatim
  11  **
  12  ** \brief The trust node utility
  13  **/
  14
  15 #include "cvc4_private.h"
  16
  17 #ifndef CVC4__THEORY__TRUST_NODE_H
  18 #define CVC4__THEORY__TRUST_NODE_H
  19
  20 #include "expr/node.h"
  21
  22 namespace CVC4 {
  23
  24 class ProofGenerator;
  25
  26 namespace theory {
  27
  28 /** A kind for trust nodes */
  29 enum class TrustNodeKind : uint32_t
  30 {
  31   CONFLICT,
  32   LEMMA,
  33   PROP_EXP,
  34   REWRITE,
  35   INVALID
  36 };
  37 /**
  38  * Converts a proof rule to a string. Note: This function is also used in
  39  * `safe_print()`. Changing this function name or signature will result in
  40  * `safe_print()` printing "<unsupported>" instead of the proper strings for
  41  * the enum values.
  42  *
  43  * Returns a string with static lifetime: it should not be freed.
  44  *
  45  * @param tnk The trust node kind
  46  * @return The name of the trust node kind
  47  */
  48 const char* toString(TrustNodeKind tnk);
  49
  50 /**
  51  * Writes a trust node kind name to a stream.
  52  *
  53  * @param out The stream to write to
  54  * @param tnk The trust node kind to write to the stream
  55  * @return The stream
  56  */
  57 std::ostream& operator<<(std::ostream& out, TrustNodeKind tnk);
  58
  59 /**
  60  * A trust node is a pair (F, G) where F is a formula and G is a proof
  61  * generator that can construct a proof for F if asked.
  62  *
  63  * More generally, a trust node is any node that can be used for a specific
  64  * purpose that requires justification, such as being passed to
  65  * OutputChannel::lemma. That justification is intended to be given by the
  66  * generator that is required to construct this object.
  67  *
  68  * They are intended to be constructed by ProofGenerator objects themselves (a
  69  * proof generator wraps itself in TrustNode it returns) and passed
  70  * to ProofOutputChannel by theory solvers.
  71  *
  72  * The static functions for constructing them check that the generator, if
  73  * provided, is capable of proving the given conflict or lemma, or an assertion
  74  * failure occurs. Otherwise an assertion error is given.
  75  *
  76  * While this is not enforced, a `TrustNode` generally encapsulates a **closed** proof
  77  * of the formula: one without free assumptions.
  78  */
  79 class TrustNode
  80 {
  81  public:
  82   TrustNode() : d_tnk(TrustNodeKind::INVALID), d_gen(nullptr) {}
  83   /** Make a proven node for conflict */
  84   static TrustNode mkTrustConflict(Node conf, ProofGenerator* g = nullptr);
  85   /** Make a proven node for lemma */
  86   static TrustNode mkTrustLemma(Node lem, ProofGenerator* g = nullptr);
  87   /** Make a proven node for explanation of propagated literal */
  88   static TrustNode mkTrustPropExp(TNode lit,
  89                                   Node exp,
  90                                   ProofGenerator* g = nullptr);
  91   /** Make a proven node for rewrite */
  92   static TrustNode mkTrustRewrite(TNode n,
  93                                   Node nr,
  94                                   ProofGenerator* g = nullptr);
  95   /** The null proven node */
  96   static TrustNode null();
  97   ~TrustNode() {}
  98   /** get kind */
  99   TrustNodeKind getKind() const;
 100   /** get node
 101    *
 102    * This is the node that is used in a common interface, either:
 103    * (1) A T-unsat conjunction conf to pass to OutputChannel::conflict,
 104    * (2) A valid T-formula lem to pass to OutputChannel::lemma,
 105    * (3) A conjunction of literals exp to return in Theory::explain(lit), or
 106    * (4) A result of rewriting a term n into an equivalent one nr.
 107    *
 108    * Notice that this node does not necessarily correspond to a valid formula.
 109    * The call getProven() below retrieves a valid formula corresponding to
 110    * the above calls.
 111    */
 112   Node getNode() const;
 113   /** get proven
 114    *
 115    * This is the corresponding formula that is proven by the proof generator
 116    * for the above cases:
 117    * (1) (not conf), for conflicts,
 118    * (2) lem, for lemmas,
 119    * (3) (=> exp lit), for propagations from explanations,
 120    * (4) (= n nr), for results of rewriting.
 121    *
 122    * When constructing this trust node, the proof generator should be able to
 123    * provide a proof for this fact.
 124    */
 125   Node getProven() const;
 126   /** get generator */
 127   ProofGenerator* getGenerator() const;
 128   /** is null? */
 129   bool isNull() const;
 130
 131   /** Get the proven formula corresponding to a conflict call */
 132   static Node getConflictProven(Node conf);
 133   /** Get the proven formula corresponding to a lemma call */
 134   static Node getLemmaProven(Node lem);
 135   /** Get the proven formula corresponding to explanations for propagation */
 136   static Node getPropExpProven(TNode lit, Node exp);
 137   /** Get the proven formula corresponding to a rewrite */
 138   static Node getRewriteProven(TNode n, Node nr);
 139
 140  private:
 141   TrustNode(TrustNodeKind tnk, Node p, ProofGenerator* g = nullptr);
 142   /** The kind */
 143   TrustNodeKind d_tnk;
 144   /** The proven node */
 145   Node d_proven;
 146   /** The generator */
 147   ProofGenerator* d_gen;
 148 };
 149
 150 /**
 151  * Writes a trust node to a stream.
 152  *
 153  * @param out The stream to write to
 154  * @param n The trust node to write to the stream
 155  * @return The stream
 156  */
 157 std::ostream& operator<<(std::ostream& out, TrustNode n);
 158
 159 }  // namespace theory
 160 }  // namespace CVC4
 161
 162 #endif /* CVC4__THEORY__TRUST_NODE_H */