Theorem a1i ≪ | index | src | ≫ 

theorem a1i (a b: wff): $ b $ > $ a -> b $;
StepHypRefExpression
1 ax_1 
b -> a -> b
2 hyp h 
b
3 1, 2 ax_mp 
a -> b

Axiom use

axs_prop_calc (ax_1, ax_mp)