356 lines
6.6 KiB
C
356 lines
6.6 KiB
C
#include <stdlib.h>
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#include <stdio.h>
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#include "term.h"
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#include "termlist.h"
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#include "substitution.h"
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#include "mgu.h"
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#include "memory.h"
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/*
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Most General Unifier
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Unification etc.
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New version yields a termlist with substituted variables, which can later be reset to NULL.
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*/
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//! Global constant. If true, typed checking
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/**
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* Analoguous to sys->match
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* 0 typed
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* 1 basic typeflaws
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* 2 all typeflaws
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*/
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int mgu_match = 0;
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extern Term TERM_Hidden;
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void
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showSubst (Term t)
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{
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#ifdef DEBUG
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if (!DEBUGL (5))
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return;
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indent ();
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printf ("Substituting ");
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termPrint (t);
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printf (", typed ");
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termlistPrint (t->stype);
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if (realTermLeaf (t->subst))
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{
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printf ("->");
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termlistPrint (t->subst->stype);
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}
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else
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{
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printf (", composite term");
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}
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if (t->type != VARIABLE)
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{
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printf (" (bound roleconstant)");
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}
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printf ("\n");
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#endif
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}
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//! See if a substitution is valid
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__inline__ int
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goodsubst (Term tvar, Term tsubst)
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{
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if (tvar->stype == NULL || (mgu_match == 2))
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{
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return 1;
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}
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else
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{
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/**
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* Check if each type of the substitution is allowed in the variable
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*/
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if (!realTermLeaf (tsubst))
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{
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// Typed var cannot match with non-leaf
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return 0;
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}
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else
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{
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// It's a leaf, but what type?
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if (mgu_match == 1
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|| termlistContained (tvar->stype, tsubst->stype))
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{
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return 1;
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}
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else
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{
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#ifdef DEBUG
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if (DEBUGL (5))
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{
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eprintf ("Substitution fails on ");
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termPrint (tvar);
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eprintf (" -/-> ");
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termPrint (tsubst);
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eprintf (", because type: \n");
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termlistPrint (tvar->stype);
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eprintf (" does not contain ");
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termlistPrint (tsubst->stype);
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eprintf ("\n");
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}
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#endif
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return 0;
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}
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}
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}
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}
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//! Undo all substitutions in a list of variables.
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/**
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* The termlist should contain only variables.
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*/
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void
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termlistSubstReset (Termlist tl)
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{
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while (tl != NULL)
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{
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tl->term->subst = NULL;
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tl = tl->next;
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}
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}
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//! Most general unifier.
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/**
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* Try to determine the most general unifier of two terms.
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* Resulting termlist must be termlistDelete'd.
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*
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*@return Returns a list of variables, that were previously open, but are now closed
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* in such a way that the two terms unify. Returns \ref MGUFAIL if it is impossible.
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*/
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Termlist
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termMguTerm (Term t1, Term t2)
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{
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/* added for speed */
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t1 = deVar (t1);
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t2 = deVar (t2);
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if (t1 == t2)
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return NULL;
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if (!(hasTermVariable (t1) || hasTermVariable (t2)))
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{
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if (isTermEqual (t1, t2))
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{
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return NULL;
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}
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else
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{
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return MGUFAIL;
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}
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}
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/* symmetrical tests for single variable */
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if (realTermVariable (t2))
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{
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if (termSubTerm (t1, t2) || !goodsubst (t2, t1))
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return MGUFAIL;
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else
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{
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t2->subst = t1;
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#ifdef DEBUG
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showSubst (t2);
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#endif
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return termlistAdd (NULL, t2);
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}
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}
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if (realTermVariable (t1))
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{
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if (termSubTerm (t2, t1) || !goodsubst (t1, t2))
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return MGUFAIL;
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else
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{
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t1->subst = t2;
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#ifdef DEBUG
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showSubst (t1);
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#endif
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return termlistAdd (NULL, t1);
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}
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}
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/* left & right are compounds with variables */
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if (t1->type != t2->type)
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return MGUFAIL;
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/* identical compounds */
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/* encryption first */
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if (realTermEncrypt (t1))
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{
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Termlist tl1, tl2;
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tl1 = termMguTerm (TermKey (t1), TermKey (t2));
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if (tl1 == MGUFAIL)
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{
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return MGUFAIL;
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}
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else
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{
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tl2 = termMguTerm (TermOp (t1), TermOp (t2));
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if (tl2 == MGUFAIL)
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{
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termlistSubstReset (tl1);
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termlistDelete (tl1);
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return MGUFAIL;
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}
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else
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{
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return termlistConcat (tl1, tl2);
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}
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}
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}
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/* tupling second
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non-associative version ! TODO other version */
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if (isTermTuple (t1))
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{
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Termlist tl1, tl2;
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tl1 = termMguTerm (TermOp1 (t1), TermOp1 (t2));
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if (tl1 == MGUFAIL)
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{
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return MGUFAIL;
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}
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else
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{
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tl2 = termMguTerm (TermOp2 (t1), TermOp2 (t2));
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if (tl2 == MGUFAIL)
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{
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termlistSubstReset (tl1);
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termlistDelete (tl1);
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return MGUFAIL;
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}
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else
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{
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return termlistConcat (tl1, tl2);
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}
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}
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}
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return MGUFAIL;
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}
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//! Most general interm unifiers of t1 interm t2
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/**
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* Try to determine the most general interm unifiers of two terms.
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*@returns Nothing. Iteration gets termlist of substitutions.
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*/
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int
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termMguInTerm (Term t1, Term t2, int (*iterator) (Termlist))
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{
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Termlist tl;
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int flag;
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flag = 1;
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t2 = deVar (t2);
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if (t2 != NULL)
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{
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if (realTermTuple (t2))
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{
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// t2 is a tuple, consider interm options as well.
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flag = flag && termMguInTerm (t1, TermOp1 (t2), iterator);
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flag = flag && termMguInTerm (t1, TermOp2 (t2), iterator);
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}
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// simple clause or combined
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tl = termMguTerm (t1, t2);
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if (tl != MGUFAIL)
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{
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// Iterate
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flag = flag && iterator (tl);
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// Reset variables
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termlistSubstReset (tl);
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// Remove list
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termlistDelete (tl);
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}
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}
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else
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{
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if (deVar (t1) != NULL)
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{
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flag = 0;
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}
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}
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return flag;
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}
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//! Most general subterm unifiers of t1 subterm t2
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/**
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* Try to determine the most general subterm unifiers of two terms.
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*@returns Nothing. Iteration gets termlist of subst, and list of keys needed to decrypt.
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*/
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int
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termMguSubTerm (Term t1, Term t2, int (*iterator) (Termlist, Termlist),
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Termlist inverses, Termlist keylist)
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{
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int flag;
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flag = 1;
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t1 = deVar (t1);
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t2 = deVar (t2);
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if (t2 != NULL)
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{
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Termlist tl;
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if (!realTermLeaf (t2))
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{
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if (realTermTuple (t2))
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{
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// 'simple' tuple
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flag =
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flag && termMguSubTerm (t1, TermOp1 (t2), iterator, inverses,
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keylist);
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flag =
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flag && termMguSubTerm (t1, TermOp2 (t2), iterator, inverses,
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keylist);
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}
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else
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{
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// Must be encryption
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// So, we need the key, and try to get the rest
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Term newkey;
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newkey = inverseKey (inverses, TermKey (t2));
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// We can never produce the TERM_Hidden key, thus, this is not a valid iteration.
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if (!isTermEqual (newkey, TERM_Hidden))
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{
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Termlist keylist_new;
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keylist_new = termlistShallow (keylist);
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keylist_new = termlistAdd (keylist_new, newkey);
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// Recurse
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flag =
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flag
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&& termMguSubTerm (t1, TermOp (t2), iterator, inverses,
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keylist_new);
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termlistDelete (keylist_new);
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}
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termDelete (newkey);
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}
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}
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// simple clause or combined
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tl = termMguTerm (t1, t2);
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if (tl != MGUFAIL)
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{
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// Iterate
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flag = flag && iterator (tl, keylist);
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// Reset variables
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termlistSubstReset (tl);
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// Remove list
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termlistDelete (tl);
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}
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}
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else
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{
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if (t1 != NULL)
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{
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flag = 0;
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}
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}
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return flag;
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}
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