Theorem tbw-ax3

Description: The third of four axioms in the Tarski-Bernays-Wajsberg system. (Contributed by Anthony Hart, 13-Aug-2011) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	tbw-ax3	$$⊢\left(\left(\phi \to \psi \right)\to \phi \right)\to \phi$$

Proof

Step	Hyp	Ref	Expression
1		peirce	$$⊢\left(\left(\phi \to \psi \right)\to \phi \right)\to \phi$$