The directive 'external' is used to declare the existence of predicates in an external package

As a result of the declaration, the compiler will not complain about missing predicates, and at runtime the package file will be loaded dynamically when the external predicates are first accessed.

For collections of predicates, use the directive 'package'

:- external(bb,[b/1,b/2]).


a(Z) :-
	b(X), b(X,Z).