Description: In classical logic all wffs are testable, that is, it is always true that
( -. ph \/ -. -. ph ) . This is not necessarily true in
intuitionistic logic. In intuitionistic logic, if this statement is true
for some ph , then ph istestable. The proof is trivial because
it's simply a special case of the law of the excluded middle, which is
true in classical logic but not necessarily true in intuitionisic logic.
(Contributed by David A. Wheeler, 5-Dec-2018)