
instance(?Instance, ?Term)

   Succeeds if Instance is an instance of Term.



Arguments
   Instance            An arbitrary term.
   Term                An arbitrary term.

Type
   Comparing and Sorting

Description
   Succeeds if it is possible to find an instantiation of free variables in
   Term such that Term and Instance are equal.  The result is undefined if
   Term and Instance share variables.  Note that no unification actually
   occurs.

   Attributed variables are handled via the attribute's compare_instances
   handler.  In particular, domain variables should be handled correctly.



Modes and Determinism
   instance(?, ?) is semidet

Fail Conditions
   Fails if Instance is not an instance of Term.

Examples
   
   Success:
   instance(atom,X).
   instance(f(a,b),X).
   instance(f(a,b),f(X,Y)).
   instance(f(a,X),f(Y,X)).
   instance(f(a,X),f(X,Y)).
   instance(f(X,Y),f(Y,X)).
   instance([a,b,c],[A,B,C]).
   instance([a,f(1,b,X),Y|Z],T).
   X::1..5, instance(3,X).
   X::2..4, Y::1..5, instance(X,Y).

   Fail:
   instance(f(a,b),f(X,X)).
   instance(X,a).
   X::2..4, Y::1..5, instance(Y,X).


See Also
   compare_instances / 3, prune_instances / 2, variant / 2
