Links to most papers, project, and research events in this area can be found here. KIF is based on predicate logic but provides a Lisp-oriented syntax for it. Object constants are used to denote individual objects. Function constants denote functions on those objects. Relation constants denote relations.
Logical constants express conditions about the world and are either true or false.
This feature allows the reification of formulas as terms used in other formulas, making it possible to make statements over statements.