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/* Copyright (C) 2006, 2007 William McCune
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This file is part of the LADR Deduction Library.
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The LADR Deduction Library is free software; you can redistribute it
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and/or modify it under the terms of the GNU General Public License,
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The LADR Deduction Library is distributed in the hope that it will be
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useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with the LADR Deduction Library; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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This package implements two kinds of discrimination indexing
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for first-order terms. Both kinds support GENERALIZATION retrieval
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only (e.g., for forward demodulation and forward subsumption).
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The "wild" kind is an imperfect filter, and it does not bind variables.
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The caller must also call a routine, say match(), to check if
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the answers are really more general than the query term and to
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construct the substitution.
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Wild indexing supports associative-commutative (AC) and
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commutative (C) symbols.
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Indexing terms with AC symbols works by considering the number
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of arguments and the number of nonvariable arguments of
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AC terms that do not occur in other AC terms.
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(The term "wild" is used because all variables in the discrimination
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tree are treated as the the wildcard symbol *).
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With the "bind" kind, every answer is more general than the query term,
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and the matching substitution is constructed during the retrieval.
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Wild indexing supports commutative (C) symbols,
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but it <I>does not support</I> associative-commutative (AC) symbols.
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Retrieval with C symbols can produce duplicate answers.
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There is probably a higher-level package (mindex ?) which
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provides a uniform interface to these and other indexing methods.
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/* Public definitions */
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typedef struct discrim * Discrim;
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struct discrim { /* node in a discrimination tree */
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Discrim next; /* sibling */
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Discrim kids; /* for internal nodes */
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Plist data; /* for leaves */
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short symbol; /* variable number or symbol number */
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char type; /* term type and for ac indexing type */
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typedef struct discrim_pos * Discrim_pos;
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struct discrim_pos { /* to save position in set of answers */
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Context subst; /* substitution */
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Plist data; /* identical terms from leaf of discrim tree */
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void *backtrack; /* data for backtracking */
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/* type of discrimination tree node */
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enum { DVARIABLE, DRIGID, AC_ARG_TYPE, AC_NV_ARG_TYPE };
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#define DVAR(d) ((d)->type == DVARIABLE)
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/* End of public definitions */
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/* Public function prototypes from discrim.c */
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Discrim get_discrim(void);
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void free_discrim(Discrim p);
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Discrim_pos get_discrim_pos(void);
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void free_discrim_pos(Discrim_pos p);
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void fprint_discrim_mem(FILE *fp, BOOL heading);
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void p_discrim_mem(void);
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Discrim discrim_init(void);
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void discrim_dealloc(Discrim d);
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void destroy_discrim_tree(Discrim d);
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BOOL discrim_empty(Discrim d);
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#endif /* conditional compilation of whole file */
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ladr/discrim.h.bak
