A Useful Four-Valued Logic

Belnap’s 1977 A Useful Four-Valued Logic, published in Modern Uses of Multiple-Valued Logic, is one of the program’s working technical references. Cited in Book I (Categorical Foundations), Part 12, Chapter Four Truth Values from Polarity Stabilization, where the program draws on it in the context of “The four truth values are not postulated as in Belnap’s four-valued logic FOUR , nor are they introduced by philosophical decree.”