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`library(varnumbers)`

The built-in predicate `numbervars/3`

makes a term
ground by binding the variables in it to subterms of the form `'$VAR'(`

where `N`)`N` is an integer. Most of the calls to `numbervars/3`

look like

numbervars(Term, 0, _)

which can be abbreviated to

numbervars(Term)

if you use this package.

`varnumbers/3`

is a partial inverse to `numbervars/3`

:

varnumbers(Term, N0, Copy)

unifies `Copy` with a copy of `Term` in which subterms of the form
`'$VAR'(`

where `N`)`N` is an integer not less than `N0` (that is, subterms
which might have been introduced by `numbervars/3`

with second argument
`N0`) have been consistently replaced by new variables. Since 0 is the
usual second argument of `numbervars/3`

, there is also

varnumbers(Term, Copy)

This provides a facility whereby a Prolog-like data base can be
kept as a term. For example, we might represent `append/3`

thus:

Clauses = [ (append([], '$VAR'(0), '$VAR'(0)) :- true), (append(['$VAR'(0)|'$VAR'(1), '$VAR'(2), ['$VAR'(0)|'$VAR(3)]) :- append('$VAR'(1), '$VAR'(2), '$VAR'(3))) ]

and we might access clauses from it by doing

prove(Goal, Clauses) :- member(Clause, Clauses), varnumbers(Clause, (Goal:-Body)), prove(Goal).

Exported predicates:

`numbervars(`

`+Term`)-
makes

`Term`ground by binding variables to subterms`'$VAR'(`

with values of`N`)`N`ranging from 0 up. `varnumbers(`

`+Term`,`-Copy`)-
succeeds when

`Term`was a term producing by calling`numbervars(`

and`Term`)`Copy`is a copy of`Term`with such subterms replaced by variables. `varnumbers(`

`+Term`,`+N0`,`-Copy`)succeeds when

`Term`was a term produced by calling`numbervars(`

(so that all subterms`Term`,`N0`,`N`)`'$VAR'(`

have`X`)`integer(`

,`X`)

) and`X`>=`N0``Copy`is a copy of`Term`with such subterms replaced by variables.

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