I think he probably spoke about "Designing and Programming Personal Expert Systems" by Carl Townsend that dates back to 1986.

From http://www.faqs.org/faqs/computer-lang/forth-faq/part5/

  Contains LISP and Prolog emulations in Forth, 
  including a unification   algorithm.  It also has some
  minimum distance classifier code. 
  The application is fault diagnosis in locomotives.