Theorem retbwax3

Description: tbw-ax3 rederived from merco1 . (Contributed by Anthony Hart, 17-Sep-2011) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	retbwax3	$$⊢\left(\left(\phi \to \psi \right)\to \phi \right)\to \phi$$

Proof

Step	Hyp	Ref	Expression
1		retbwax2	$$⊢\phi \to \left(\phi \to \phi \right)$$
2		merco1lem7	$$⊢\left(\phi \to \left(\phi \to \phi \right)\right)\to \left(\left(\left(\phi \to \psi \right)\to \phi \right)\to \phi \right)$$
3	1 2	ax-mp	$$⊢\left(\left(\phi \to \psi \right)\to \phi \right)\to \phi$$