Theorem bior2a ≪ | index | src | ≫ 

theorem bior2a (a b: wff): $ (b -> a) -> (a \/ b <-> a) $;
StepHypRefExpression
1 orcomb 
a \/ b <-> b \/ a
2 bior1a 
(b -> a) -> (b \/ a <-> a)
3 1, 2 syl5bb 
(b -> a) -> (a \/ b <-> a)

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)