Theorem bith ≪ | index | src | ≫

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

Step	Hyp	Ref	Expression
1		anl	a /\ b -> a
2		anr	a /\ b -> b
3	1, 2	bithd	a /\ b -> (a <-> b)
4	3	exp	a -> b -> (a <-> b)

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)