Theorem con3bb | index | src |

theorem con3bb (a b: wff): $ a <-> b <-> (~a <-> ~b) $;
StepHypRefExpression
1 con3b
(a <-> b) -> (~a <-> ~b)
2 con4b
(~a <-> ~b) -> (a <-> b)
3 1, 2 ibii
a <-> b <-> (~a <-> ~b)

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)