Except for its belated proof of 1 + 1 = 2, Principia Mathematica doesn’t feature in studies of mathematical humour. Yet there is restrained and understated humour in that work, despite the inauspicious conditions under which it was written. Russell, to take one of the authors, had an irrepressible talent for enlivening his subject matter. This paper explores even the "obscure corners" of PM to uncover its humour and wit, which, for non-logicians, can be an entree to the work.

This paper has two aims. First, it sets out an interpretation of the relevant logic E of relevant entailment based on the theory of situated inference. Second, it uses this interpretation, together with Anderson and Belnap’s natural deduc- tion system for E, to generalise E to a range of other systems of strict relevant implication. Routley–Meyer ternary relation semantics for these systems are produced and completeness theorems are proven. -/- .