XCB, the Last of the Shortest Single Axioms for the Classical Equivalential Calculus
arXiv:cs/0211015
Abstract
It has long been an open question whether the formula XCB = EpEEEpqErqr is, with the rules of substitution and detachment, a single axiom for the classical equivalential calculus. This paper answers that question affirmatively, thus completing a search for all such eleven-symbol single axioms that began seventy years ago.
6 pages, no figures