George Boolos Sy D. Friedman Harold Hodes Meeting of the Association for Symbolic Logic: New York 1979. 427-434 1981 46 J. Symb. Log. 2 db/journals/jsyml/jsyml46.html#BoolosFH81 https://doi.org/10.2307/2273640 http://projecteuclid.org/euclid.jsl/1183740795