SA → MRTLA negated = SA and /MRTLA;

If small animal, then move more rapidly than large animal

negated = One can be small animal and not move more rapidly than large animal (which, don't forget, includes can move at the exact same rapid pace as large animal)

AA ‑m→ C negated /(AA ‑m→ C)

if appropriate analogy to.. then most(ly?) chess

negated = half or less of appropriate analogies for... are chess (analogies)

is this interpretation right too? I can derive meaning from it, like the original statement is that if something is an appropriate analogy to... then it's mostly chess. and then if it's negated then it's simply not that the case that (or, half or less of) appropriate analogies for....

if the words "no" or "none" or the phrase "it's not the case that" etc., pop up, then it falls under the rule of negating either condition and making it the necessary condition. That's why some (at least 1) A are B negated is some (at least 1) A are not B, and the contrapositive would be: B --> /A