Proof of proveit.logic.booleans.implication.iff_t_f theorem

import proveit
from proveit.logic.booleans.implication  import iff_def, implies_t_f
theory = proveit.Theory() # the theorem's theory

%proving iff_t_f

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

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

%qed

proveit.logic.booleans.implication.iff_t_f has been proven.

	step type	requirements	statement
0	instantiation	1, 2	⊢
	:
1	axiom		⊢
	proveit.logic.booleans.negation.negation_elim
2	instantiation	3, 4	⊢
	: , :
3	theorem		⊢
	proveit.logic.booleans.implication.not_iff_via_not_right_impl
4	instantiation	5, 6	⊢
	:
5	theorem		⊢
	proveit.logic.booleans.negation.negation_intro
6	axiom		⊢
	proveit.logic.booleans.implication.implies_t_f