pldoc: how to specify predicates with arguments unbound.

Hi, 

Using pldoc, how do we specify a predicate such as follows:

	foo(X, Y) :-  (random(3) =:= 2, X==Y;  true).

foo is designed so that it returns information on the current state 
on unification (constraint)   X==Y or X\==Y.  So X, and Y are always unbound 
 (var(X), var(Y) are always true).  I often wrote such predicates. 

Reading pldoc document, the following seems only possible form for foo/2.

% foo(-X, -Y)  is det.

Is it right ?  Or, is there any other neat form of specification 
to tell such intention of programmer of foo above.

Kuniaki Mukai





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