Theorem noteq ≪ | index | src | ≫

theorem noteq (a b: wff): $ (a <-> b) -> (~a <-> ~b) $;

Step	Hyp	Ref	Expression
1		con3b	(a <-> b) -> (~a <-> ~b)

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)