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# nonground(+N, ?Term, -VarList)

Succeeds if Term contains at least N different variables, and returns N of
them in the list VarList.
*N*
- Integer.
*Term*
- Prolog term.
*VarList*
- List or variable.

## Description

Used to test whether Term contains at least N different variables. The
argument VarList is unified with a list of exactly N of those variables.
If Term contains more than N variables, it is not further specified
which ones will be in the list and in which order. As usual, attributed
variables are also considered variables.
Note that this predicate is a generalisation of nonground/1 and
nonground/2 which could be written as:

nonground(Term) :- nonground(1, Term, _).
nonground(Term, Var) :- nonground(1, Term, [Var]).

This predicate can handle cyclic terms.

### Modes and Determinism

- nonground(+, ?, -) is semidet

### Fail Conditions

Fails if Term contains less than N variables
### Exceptions

*(4) instantiation fault *
- N is not instantiated.
*(5) type error *
- VarList instantiated but not to a list.
*(6) out of range *
- N is not positive.

## Examples

Success:
nonground(1, Term, L). % gives L = [Term]
nonground(1, f(a,B,c), L). % gives L = [B]
nonground(2, [X,Y,Z], L). % gives L = [Y,X]
nonground(2, [X,Y,Z], L). % gives L = [Y,X]
nonground(1, s(X{a}), L). % gives L = [X{a}]
Fail:
nonground(1, atom, L).
nonground(2, f(a,B,c), L).
nonground(2, [X,X,X], L).

## See Also

nonground / 1, nonground / 2, nonvar / 1, var / 1