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.