Proof of proveit.logic.classes.membership.fold_not_in_class theorem

import proveit
theory = proveit.Theory() # the theorem's theory

%proving fold_not_in_class

Under these presumptions, we begin our proof of
fold_not_in_class:
(see dependencies)

fold_not_in_class may now be readily provable (assuming required theorems are usable).  Simply execute "%qed".