There probably is no better illustration of the vagaries of notational fashion than the fact that nowadays, the numeral **1 **is commonly used to denote the (conceptually very important) terminal category, while George Boole 170 years ago used **1 **to denote a *universe: *

(p. 15 in George Boole, *The mathematical analysis of logic : being an essay towards a calculus of deductive reasoning, *1847, Macmillan, Cambridge)

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