When you do the contrapositive do the sufficient and necessary conditions stay with the same clause or do they switch. For example, We knew in the original sentence "When zombies attack New York City, the real estate market will crash" that "zombies attack New York City" was sufficient because it followed "when," but in the negation "If the real estate market is not crashing, then zombies are not attacking New York City" now "the real estate market is not crashing" is following "if." Does that mean that "the real estate market is not crashing" is not the sufficient condition, or is it only the sufficient condition when it is positive?

In the first example, isn't "are" just the verb and eligible would be an adjective? I don't see how eligible is a verb. Are subject complements such as eligible just counted into the predicate-verb? Same with the second example. "Are understimulated" Isn't "are" just the verb and understimulated is a subject complement/predicate adjective?