ABSTRACT
There are a number of special predicates available in Prolog which do not need definition by the user since they are provided in advance by the designers of the implementation. Such predicates are known as built-in predicates. However, the built-in predicates of most interest are those that allow access to facilities that would not be definable using a pure Prolog consisting only of facts and rules. It is these extra-logical predicates which, amongst other things, allow a program to interact with the world outside of itself. Consequently, they only admit a procedural interpretation. For example, some versions of Prolog have a number of built-in predicates for graphics. These are useful for displaying phrase structure trees but are, as yet, non-standard. This chapter only introduces those predicates which are to be found in most implementations. A drive predicate is one which controls the program by calling the main goals.
