Theorem syl6ibr | index | src |

theorem syl6ibr (a b c d: wff): $ d <-> c $ > $ a -> b -> c $ > $ a -> b -> d $;
StepHypRefExpression
1 bi2
(d <-> c) -> c -> d
2 hyp h1
d <-> c
3 1, 2 ax_mp
c -> d
4 hyp h2
a -> b -> c
5 3, 4 syl6
a -> b -> d

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)