Gary Riley was, for a long time, a NASA employee whose sole assignment seemed to be to work out the C implementation of the OPS language from LISP to C so that the military could use it. LISP, even the Symbolics LISP machine, was far too slow for practical applications. Dr. Girratano worked with Gary to produce a book that could be used as a text book in classes taught at the University of Houston and could be attended by the NASA personnel. All hand-in-glove situation that worked out quite well.

But, The Book! I have used it to teach many of my classes on AI. The first five or six chapters can be applied to ANY rulebased system. The first two chapters can be read by any person who wants to understand more about AI. True enough, most of the vendors today have directed their efforts to Java, but the speed of CLIPS is now (since about 20008) one of the fastest in the world. The power of CLIPS is unparalleled in terms of subroutines and extensions that have been implemented over the past 20 years by NASA and others.