Theorem syl5bi | index | src |

theorem syl5bi (a b c d: wff): $ b <-> c $ > $ a -> c -> d $ > $ a -> b -> d $;
StepHypRefExpression
1 bi1
(b <-> c) -> b -> c
2 hyp h1
b <-> c
3 1, 2 ax_mp
b -> c
4 hyp h2
a -> c -> d
5 3, 4 syl5
a -> b -> d

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)