`numbervars/3`

`numbervars(`

`+Term`, `+FirstVar`, `-LastVar`)

instantiates each of the variables in `Term` to a term of the form
`'$VAR'(`

.
`N`)

`Term`*term*`FirstVar`*integer*, must be nonvar`LastVar`*integer*

`FirstVar` is used as the value of `N` for the first variable
in `Term` (starting from the left). The second distinct variable
in `Term` is given a value of `N` satisfying “`N` is
`FirstVar`+1”; the third distinct variable gets the value
`FirstVar`+2, and so on. The last variable in `Term` has the
value `LastVar`-1.

Notice that in the example below, `write_canonical/1`

is used rather than
`writeq/1`

. This is because `writeq/1`

treats terms of the
form `'$VAR'(`

specially; it writes ‘`N`)`A`’ if
`N`=0, ‘`B`’ if `N`=1, …‘`Z`’ if `N`=25,
‘`A1`’ if `N`=26, etc. That is why, if you type the goal in
the example below, the variable bindings will also be printed out as
follows:

Term = foo(W,W,X), A = W, B = X

`instantiation_error`

`FirstVar`is uninstantiated`type_error`

`FirstVar`is not an integer

| ?-Term = foo(A, A, B), numbervars(Term, 22, _), write_canonical(Term).foo('$VAR'(22),'$VAR'(22),'$VAR'(23))

ref-lte-anv,
`write_term/[2,3]`

.

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