Theorem bi1d ≪ | index | src | ≫ 

theorem bi1d (a b c: wff): $ a -> (b <-> c) $ > $ a -> b -> c $;
StepHypRefExpression
1 bi1 
(b <-> c) -> b -> c
2 hyp h 
a -> (b <-> c)
3 1, 2 syl 
a -> b -> c

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)