Theorem retbwax4

Description: tbw-ax4 rederived from merco1 . (Contributed by Anthony Hart, 17-Sep-2011) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	retbwax4	$$⊢\perp \to \phi$$

Proof

Step	Hyp	Ref	Expression
1		merco1lem1	$$⊢\phi \to \left(\perp \to \phi \right)$$
2		merco1lem1	$$⊢\left(\phi \to \left(\perp \to \phi \right)\right)\to \left(\perp \to \phi \right)$$
3	1 2	ax-mp	$$⊢\perp \to \phi$$