Theorem bibi1 | index | src |

theorem bibi1 (a b: wff): $ a -> (a <-> b <-> b) $;
StepHypRefExpression
1 bi1
(a <-> b) -> a -> b
2 1 com12
a -> (a <-> b) -> b
3 bith
a -> b -> (a <-> b)
4 2, 3 ibid
a -> (a <-> b <-> b)

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)