The require/1 directive provides less control over the exact nature and location of the predicate. As autoload/2, it prevents a local definition of this predicate. As SWI-Prolog guarantees that the set of built-in predicates and predicates available for autoloading is unambiguous (i.e., has no duplicates) the specification is unambiguous. It provides four advantages over autoload/2: (1) the user does not have to remember the exact library, (2) the directive can be supported in other Prolog systems^{57SICStus provides it}, providing compatibility despite differences in library and built-in predicate organization, (3) it is robust against changes to the SWI-Prolog libraries and (4) it is less typing.