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       1                 :            : /******************************************************************************
       2                 :            :  * This file is part of the cvc5 project.
       3                 :            :  *
       4                 :            :  * Copyright (c) 2009-2026 by the authors listed in the file AUTHORS
       5                 :            :  * in the top-level source directory and their institutional affiliations.
       6                 :            :  * All rights reserved.  See the file COPYING in the top-level source
       7                 :            :  * directory for licensing information.
       8                 :            :  * ****************************************************************************
       9                 :            :  *
      10                 :            :  * Higher-order term database class.
      11                 :            :  */
      12                 :            : 
      13                 :            : #include "cvc5_private.h"
      14                 :            : 
      15                 :            : #ifndef CVC5__THEORY__QUANTIFIERS__HO_TERM_DATABASE_H
      16                 :            : #define CVC5__THEORY__QUANTIFIERS__HO_TERM_DATABASE_H
      17                 :            : 
      18                 :            : #include <map>
      19                 :            : 
      20                 :            : #include "expr/node.h"
      21                 :            : #include "theory/quantifiers/term_database.h"
      22                 :            : 
      23                 :            : namespace cvc5::internal {
      24                 :            : namespace theory {
      25                 :            : namespace quantifiers {
      26                 :            : 
      27                 :            : /**
      28                 :            :  * Higher-order term database, which extends the normal term database based on
      29                 :            :  * techniques from Barbosa et al CADE 2019.
      30                 :            :  */
      31                 :            : class HoTermDb : public TermDb
      32                 :            : {
      33                 :            :  public:
      34                 :            :   HoTermDb(Env& env, QuantifiersState& qs, QuantifiersRegistry& qr);
      35                 :            :   ~HoTermDb();
      36                 :            :   /** identify */
      37                 :          0 :   std::string identify() const override { return "HoTermDb"; }
      38                 :            :   /** get higher-order type match predicate
      39                 :            :    *
      40                 :            :    * This predicate is used to force certain functions f of type tn to appear as
      41                 :            :    * first-class representatives in the quantifier-free UF solver. For a typical
      42                 :            :    * use case, we call getHoTypeMatchPredicate which returns a fresh predicate
      43                 :            :    * P of type (tn -> Bool). Then, we add P( f ) as a lemma.
      44                 :            :    */
      45                 :            :   static Node getHoTypeMatchPredicate(TypeNode tn);
      46                 :            : 
      47                 :            :  private:
      48                 :            :   /** Performs merging of term indices based on higher-order reasoning */
      49                 :            :   bool finishResetInternal(Theory::Effort e) override;
      50                 :            :   /** add term higher-order
      51                 :            :    *
      52                 :            :    * This registers additional terms corresponding to (possibly multiple)
      53                 :            :    * purifications of a higher-order term n.
      54                 :            :    *
      55                 :            :    * Consider the example:
      56                 :            :    *    g : Int -> Int, f : Int x Int -> Int
      57                 :            :    *    constraints: (@ f 0) = g, (f 0 1) = (@ (@ f 0) 1) = 3
      58                 :            :    *    pattern: (g x)
      59                 :            :    * where @ is HO_APPLY.
      60                 :            :    * We have that (g x){ x -> 1 } is an E-match for (@ (@ f 0) 1).
      61                 :            :    * With the standard registration in addTerm, we construct term indices for
      62                 :            :    *   f, g, @ : Int x Int -> Int, @ : Int -> Int.
      63                 :            :    * However, to match (g x) with (@ (@ f 0) 1), we require that
      64                 :            :    *   [1] -> (@ (@ f 0) 1)
      65                 :            :    * is an entry in the term index of g. To do this, we maintain a term
      66                 :            :    * index for a fresh variable pfun, the purification variable for
      67                 :            :    * (@ f 0). Thus, we register the term (pfun 1) in the call to this function
      68                 :            :    * for (@ (@ f 0) 1). This ensures that, when processing the equality
      69                 :            :    * (@ f 0) = g, we merge the term indices of g and pfun. Hence, the entry
      70                 :            :    *   [1] -> (@ (@ f 0) 1)
      71                 :            :    * is added to the term index of g, assuming g is the representative of
      72                 :            :    * the equivalence class of g and pfun.
      73                 :            :    *
      74                 :            :    * Above, we additionally add the lemmas (@ f 0) = pfun and
      75                 :            :    * (pfun 1) = (@ (@ f 0) 1).
      76                 :            :    */
      77                 :            :   void addTermInternal(Node n) override;
      78                 :            :   /** Get operators that we know are equivalent to f */
      79                 :            :   void getOperatorsFor(TNode f, std::vector<TNode>& ops) override;
      80                 :            :   /** get the chosen representative for operator op */
      81                 :            :   Node getOperatorRepresentative(TNode op) const override;
      82                 :            :   /** check if we are in conflict based on congruent terms a and b */
      83                 :            :   bool checkCongruentDisequal(TNode a,
      84                 :            :                               TNode b,
      85                 :            :                               std::vector<Node>& exp) override;
      86                 :            :   //------------------------------higher-order term indexing
      87                 :            :   /**
      88                 :            :    * The set of terms that we have added higher-order term purification lemmas
      89                 :            :    * for.
      90                 :            :    */
      91                 :            :   context::CDHashSet<Node> d_hoFunOpPurify;
      92                 :            :   /** a map from matchable operators to their representative */
      93                 :            :   std::map<TNode, TNode> d_hoOpRep;
      94                 :            :   /** for each representative matchable operator, the list of other matchable
      95                 :            :    * operators in their equivalence class */
      96                 :            :   std::map<TNode, std::vector<TNode> > d_hoOpSlaves;
      97                 :            : };
      98                 :            : 
      99                 :            : }  // namespace quantifiers
     100                 :            : }  // namespace theory
     101                 :            : }  // namespace cvc5::internal
     102                 :            : 
     103                 :            : #endif /* CVC5__THEORY__QUANTIFIERS__HO_TERM_DATABASE_H */