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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]).
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