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       1                 :            : /******************************************************************************
       2                 :            :  * Top contributors (to current version):
       3                 :            :  *   Andrew Reynolds, Haniel Barbosa, Hans-Joerg Schurr
       4                 :            :  *
       5                 :            :  * This file is part of the cvc5 project.
       6                 :            :  *
       7                 :            :  * Copyright (c) 2009-2024 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.
      11                 :            :  * ****************************************************************************
      12                 :            :  *
      13                 :            :  * Proof node utility.
      14                 :            :  */
      15                 :            : 
      16                 :            : #include "cvc5_private.h"
      17                 :            : 
      18                 :            : #ifndef CVC5__PROOF__PROOF_NODE_H
      19                 :            : #define CVC5__PROOF__PROOF_NODE_H
      20                 :            : 
      21                 :            : #include <vector>
      22                 :            : 
      23                 :            : #include "expr/node.h"
      24                 :            : #include "cvc5/cvc5_proof_rule.h"
      25                 :            : 
      26                 :            : namespace cvc5::internal {
      27                 :            : 
      28                 :            : class ProofNodeManager;
      29                 :            : class ProofNode;
      30                 :            : 
      31                 :            : // Alias for shared pointer to a proof node
      32                 :            : using Pf = std::shared_ptr<ProofNode>;
      33                 :            : 
      34                 :            : struct ProofNodeHashFunction
      35                 :            : {
      36                 :            :   inline size_t operator()(std::shared_ptr<ProofNode> pfn) const;
      37                 :            :   size_t operator()(const ProofNode* pfn) const;
      38                 :            : }; /* struct ProofNodeHashFunction */
      39                 :            : 
      40                 :            : /** A node in a proof
      41                 :            :  *
      42                 :            :  * A ProofNode represents a single step in a proof. It contains:
      43                 :            :  * (1) d_id, an identifier indicating the kind of inference,
      44                 :            :  * (2) d_children, the child ProofNode objects indicating its premises,
      45                 :            :  * (3) d_args, additional arguments used to determine the conclusion,
      46                 :            :  * (4) d_proven, cache of the formula that this ProofNode proves.
      47                 :            :  *
      48                 :            :  * Overall, a ProofNode and its children form a directed acyclic graph.
      49                 :            :  *
      50                 :            :  * A ProofNode is partially mutable in that (1), (2) and (3) can be
      51                 :            :  * modified. A motivating example of when this is useful is when a ProofNode
      52                 :            :  * is established to be a "hole" for something to be proven later. On the other
      53                 :            :  * hand, (4) is intended to be immutable.
      54                 :            :  *
      55                 :            :  * The method setValue is private and can be called by objects that manage
      56                 :            :  * ProofNode objects in trusted ways that ensure that the node maintains
      57                 :            :  * the invariant above. Furthermore, notice that this class is not responsible
      58                 :            :  * for setting d_proven; this is done externally by a ProofNodeManager class.
      59                 :            :  *
      60                 :            :  * Notice that all fields of ProofNode are stored in ***Skolem form***. Their
      61                 :            :  * correctness is checked in ***witness form*** (for details on this
      62                 :            :  * terminology, see expr/skolem_manager.h). As a simple example, say a
      63                 :            :  * theory solver has a term t, and wants to introduce a unit lemma (= k t)
      64                 :            :  * where k is a fresh Skolem variable. It creates this variable via:
      65                 :            :  *   k = SkolemManager::mkPurifySkolem(t,"k");
      66                 :            :  * A checked ProofNode for the fact (= k t) then may have fields:
      67                 :            :  *   d_rule := MACRO_SR_PRED_INTRO,
      68                 :            :  *   d_children := {},
      69                 :            :  *   d_args := {(= k t)}
      70                 :            :  *   d_proven := (= k t).
      71                 :            :  * Its justification via the rule MACRO_SR_PRED_INTRO (see documentation
      72                 :            :  * in theory/builtin/proof_kinds) is in terms of the witness form of the
      73                 :            :  * argument:
      74                 :            :  *   (= (witness ((z T)) (= z t)) t)
      75                 :            :  * which, by that rule's side condition, is such that:
      76                 :            :  *   Rewriter::rewrite((= (witness ((z T)) (= z t)) t)) = true.
      77                 :            :  * Notice that the correctness of the rule is justified here by rewriting
      78                 :            :  * the witness form of (= k t). The conversion to/from witness form is
      79                 :            :  * managed by ProofRuleChecker::check.
      80                 :            :  *
      81                 :            :  * An external proof checker is expected to formalize the ProofNode only in
      82                 :            :  * terms of *witness* forms.
      83                 :            :  *
      84                 :            :  * However, the rest of cvc5 sees only the *Skolem* form of arguments and
      85                 :            :  * conclusions in ProofNode, since this is what is used throughout cvc5.
      86                 :            :  */
      87                 :            : class ProofNode
      88                 :            : {
      89                 :            :   friend class ProofNodeManager;
      90                 :            : 
      91                 :            :  public:
      92                 :            :   ProofNode(ProofRule id,
      93                 :            :             const std::vector<std::shared_ptr<ProofNode>>& children,
      94                 :            :             const std::vector<Node>& args);
      95                 :  122624000 :   ~ProofNode() {}
      96                 :            :   /** get the rule of this proof node */
      97                 :            :   ProofRule getRule() const;
      98                 :            :   /** Get children */
      99                 :            :   const std::vector<std::shared_ptr<ProofNode>>& getChildren() const;
     100                 :            :   /** Get arguments */
     101                 :            :   const std::vector<Node>& getArguments() const;
     102                 :            :   /** get what this node proves, or the null node if this is an invalid proof */
     103                 :            :   Node getResult() const;
     104                 :            :   /**
     105                 :            :    * Returns true if this is a closed proof (i.e. it has no free assumptions).
     106                 :            :    */
     107                 :            :   bool isClosed();
     108                 :            :   /** Print debug on output strem os
     109                 :            :    *
     110                 :            :    * @param os the stream to print to
     111                 :            :    * @param printConclusion Whether to print conclusions
     112                 :            :    */
     113                 :            :   void printDebug(std::ostream& os, bool printConclusion = false) const;
     114                 :            :   /**
     115                 :            :    * Clone this proof node, which creates a deep copy of this proof node and
     116                 :            :    * returns it. The dag structure of pn is the same as that in the returned
     117                 :            :    * proof node.
     118                 :            :    *
     119                 :            :    * @return the cloned proof node.
     120                 :            :    */
     121                 :            :   std::shared_ptr<ProofNode> clone() const;
     122                 :            : 
     123                 :            :  private:
     124                 :            :   /**
     125                 :            :    * Set value, called to overwrite the contents of this ProofNode with the
     126                 :            :    * given arguments.
     127                 :            :    */
     128                 :            :   void setValue(ProofRule id,
     129                 :            :                 const std::vector<std::shared_ptr<ProofNode>>& children,
     130                 :            :                 const std::vector<Node>& args);
     131                 :            :   /** The proof rule */
     132                 :            :   ProofRule d_rule;
     133                 :            :   /** The children of this proof node */
     134                 :            :   std::vector<std::shared_ptr<ProofNode>> d_children;
     135                 :            :   /** arguments of this node */
     136                 :            :   std::vector<Node> d_args;
     137                 :            :   /** The cache of the fact that has been proven, modifiable by ProofChecker */
     138                 :            :   Node d_proven;
     139                 :            :   /** Was d_proven actually checked, or is it trusted? */
     140                 :            :   bool d_provenChecked;
     141                 :            : };
     142                 :            : }  // namespace cvc5::internal
     143                 :            : 
     144                 :            : namespace std {
     145                 :            : template <>
     146                 :            : struct hash<cvc5::internal::ProofNode>
     147                 :            : {
     148                 :            :   size_t operator()(const cvc5::internal::ProofNode& node) const;
     149                 :            : };
     150                 :            : }  // namespace std
     151                 :            : 
     152                 :            : namespace cvc5::internal {
     153                 :            : 
     154                 :    2425150 : inline size_t ProofNodeHashFunction::operator()(
     155                 :            :     std::shared_ptr<ProofNode> pfn) const
     156                 :            : {
     157                 :    2425150 :   return pfn->getResult().getId() + static_cast<unsigned>(pfn->getRule());
     158                 :            : }
     159                 :            : 
     160                 :            : /**
     161                 :            :  * Serializes a given proof node to the given stream.
     162                 :            :  *
     163                 :            :  * @param out the output stream to use
     164                 :            :  * @param pn the proof node to output to the stream
     165                 :            :  * @return the stream
     166                 :            :  */
     167                 :            : std::ostream& operator<<(std::ostream& out, const ProofNode& pn);
     168                 :            : 
     169                 :            : }  // namespace cvc5::internal
     170                 :            : 
     171                 :            : #endif /* CVC5__PROOF__PROOF_NODE_H */