Theorem con2d ≪ | index | src | ≫ 

theorem con2d (a b c: wff): $ a -> b -> ~c $ > $ a -> c -> ~b $;
StepHypRefExpression
1 con2 
(b -> ~c) -> c -> ~b
2 hyp h 
a -> b -> ~c
3 1, 2 syl 
a -> c -> ~b

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)