yap-6.3/docs/md/builtins.md

@defgroup builtins YAP Core Built-ins

@brief This chapter describes the core built-in predicates that control the execution of Prolog programs, provide fundamental functionality such as termm manipulation or arithmetic, and support interaction with external resources,

Many of the predicates described here have been standardised by the International Standard Organization. The corresponding standartised subset of Prolog also known as ISO-Prolog.
In the description of the arguments of predicates the following notation will be used:

• a preceding plus sign will denote an argument as an "input argument" - the argument is read, not written, and it cannot be a free variable at the time of the call;
• a preceding minus sign will denote an "output argument";
• an argument with no preceding symbol can be used in both ways.