6.11 Reserved Modules and using the‘user' module

As mentioned above, SWI-Prolog contains two special modules. The first one is the module system. This module contains all built-in predicates. Module system has no import module. The second special module is the module user. This module forms the initial working space of the user. Initially it is empty. The import module of module user is system, making all built-in predicates available.

All other modules import from the module user. This implies they can use all predicates imported into user without explicitly importing them. If an application loads all modules from the user module using use_module/1, one achieves a scoping system similar to the C-language, where every module can access all exported predicates without any special precautions.