Proof of proveit.numbers.number_sets.integers.nonzero_nonpos_int_is_neg_int theorem

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

%proving nonzero_nonpos_int_is_neg_int

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

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