theorem syl6ib (a b c d: wff): $ c <-> d $ > $ a -> b -> c $ > $ a -> b -> d $;
| Step | Hyp | Ref | Expression |
|---|
| 1 |
|
bi1 |
(c <-> d) -> c -> d |
| 2 |
|
hyp h1 |
c <-> d |
| 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)