Copycat is a model of analogy making and human cognition based on the concept of the parallel terraced scan, developed by Douglas Hofstadter, Melanie Mitchell, and others at the at http://www.cogsci.indiana.edu Center for Research on Concepts and Cognition, Indiana University Bloomington. Copycat is written in an old version of Common Lisp and will not run on modern Common Lisp interpreters.