Algebra, Meaning, and Computation: Essays dedicated to Joseph A. Goguen on the Occasion of His 65th Birthday, Kokichi Futatsugi, Jean-Pierre Jouannaud, José Meseguer, eds. Berlin, Germany: Springer-Verlag, 2006, pp. 31-49.
http://groups.csail.mit.edu/icelab/sites/default/files/pdf/harrell-metalogic-book-chapter.pdf