Theorem id ≪ | index | src | ≫

theorem id (a: wff): $ a -> a $;

Step	Hyp	Ref	Expression
1		ax_1	a -> a -> a
2		ax_1	a -> (a -> a) -> a
3	1, 2	mpd	a -> a

Axiom use

axs_prop_calc (ax_1, ax_2, ax_mp)