Besides provoking reactions in the form of rival philosophies of mathematics, the work of Whitehead and Russell stimulated new technical developments. For example, although Whitehead and Russell made free use, in Principia Mathematica, of the notions of truth-value and truth-function, they failed to incorporate these notions into a systematic technique for evaluating formulas of the propositional calculus. Such a technique, the method of truth tables, was presented by Emil Post (1897–1954) in his dissertation of 1920, published as "Introduction to a General Theory of Elementary Propositions" in the American Journal of Mathematics (43: 163–185) in 1921, the year in which Wittgenstein independently presented the same method in his Tractatus Logico-Philosophicus. The method dates back, in fact, to Peirce, but Post considered truth tables in their application not only to classical logic but also to systems in which any number of values are allowed, the primitive connectives of Principia Mathematica, "∼" and "∨," having in these...