
nonground(+N, ?Term, -VarList)

   Succeeds if Term contains at least N different variables, and returns N of
them in the list VarList.



Arguments
   N                   Integer.
   Term                Prolog term.
   VarList             List or variable.

Type
   Type Testing

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 --- N is not instantiated.
     5 --- VarList instantiated but not to a list.
     6 --- 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
