>>There is a much easier way. See below.<<

Dan, thanks, I didn't realize you had a contrapositive
rule as one of the primitives, it will certainly help
in some circumstances.

Anyway, I wasn't really looking for an easier way - we
could just use a Proof by Contradiction to do that -
but rather some way of completing the proof the way it
was written, using CASES or something similar. Is
that possible?


Regards,



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