Theorem biim2 | index | src |

theorem biim2 (a b: wff): $ ~b -> (a -> b <-> ~a) $;
StepHypRefExpression
1 biim2a
(b -> ~a) -> (a -> b <-> ~a)
2 absurd
~b -> b -> ~a
3 1, 2 syl
~b -> (a -> b <-> ~a)

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)