Theorem impd ≪ | index | src | ≫ 

theorem impd (a b c d: wff): $ a -> b -> c -> d $ > $ a -> b /\ c -> d $;
StepHypRefExpression
1 impexp 
b /\ c -> d <-> b -> c -> d
2 hyp h 
a -> b -> c -> d
3 1, 2 sylibr 
a -> b /\ c -> d

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)