The appellant is taking the universal negative proposition, “No motile sperm are pre-11:11 (in terms of ejaculation)—No A is B—and attempting to infer the so-called contrapositive of that proposition, to wit, No non-motile sperm are post 11:11—(in purer terms, non-pre 11:11)—No non-A is non-B. By the laws of logic, however, the inference of the contrapositive is invalid where the starting proposition, as in the case at bar, is a universal negative.6

Ruggero J. Aldisert, Agatha D. Aldisert, Logic for Lawyers- A Guide …, loc. 907