Theorem mtbird ≪ | index | src | ≫

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

Step	Hyp	Ref	Expression
1		hyp h2	a -> ~b
2		hyp h1	a -> (c <-> b)
3	2	bi1d	a -> c -> b
4	1, 3	mtd	a -> ~c

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)