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# copy_term_vars(?Vars, ?OldTerm, -NewTerm)

NewTerm gets unified with a variant of OldTerm where all occurrences of variables in Vars are replaced by fresh variables.

Vars
  Prolog term, usually a variable or a list of variables.
OldTerm
  Prolog term.
NewTerm
  Prolog term.

## Description

A copy of OldTerm is created, ie. a term that is similar to OldTerm but all occurrences of the variables mentioned in Vars have been replaced by new variables which do not occur elsewhere.

Attributed variables are treated like normal variables, except that their attributes are copied as specified by the corresponding copy_term handler. This would usually imply that properties of the variable which can be interpreted as unary constraints (such as its domain) are copied, while attributes that link the variable to other variables or objects are ignored.

Subterms that do not contain any of the variables to replace are not physically copied.

Note that when the structure of the term to be copied is known, then it is more efficient to use specialised unification code to do the job.

### Modes and Determinism

- copy_term_vars(?, ?, -) is det

## Examples

       [eclipse]: Term=s(X,Y,Z), copy_term_vars(Y, Term, Copy).
       X = _79
       Z = _81
       Y = _60
       Term = s(_79, _60, _81)
       Copy = s(_79, _120, _81)
       yes.

## See Also

copy_term / 2, copy_term / 3, variant / 2, functor / 3, term_variables / 2