Predicates : Testing Relations and Properties

The concept of predicate refers to a property, or to a relation between the terms of a proposition.

A predicates is a boolean operators : it is a function which tests for a condition involving its arguments. If the condition is fulfilled, the operator returns "true" or "false" – "yes" or "no".

In Lisp, "nil" means "false", and "t" means "true". As a convention, any non nil value is also interpreted as "true".

There are several types of predicates. Among these, algebraic predicates compare numbers, equality predicates test if two objects are identical, type predicates that test if an object belongs to a specific type, and so on.

In OM, predicates are often used as conditions for the execution of a program.