Proof of proveit.numbers.addition.subtraction.sub_one_is_nat theorem

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

%proving sub_one_is_nat

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

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