Proof of proveit.logic.sets.functions.injections.disjoint_set_images_are_disjoint theorem

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

%proving disjoint_set_images_are_disjoint

With these allowed/disallowed theorem/theory presumptions (e.g., to avoid circular dependencies), we begin our proof of
disjoint_set_images_are_disjoint:
(see dependencies)