we learned in Math class in school. I haven't been over them in quite a while. I suppose if I google "contrapositive" I'd find all the correct ways to restate a proposition. For instance, I'd like to verify if this is a proper corollary - or a true restatement (this is an alternative to the previous phrase, not a clarification of it) - of the Golden Rule: you are to be treated as you treat others.
It strikes me as a more useful moral tenet.