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	|- ( ( ( ph -> ps ) -> ph ) -> ph )

Proof

Step	Hyp	Ref	Expression
1		peirce	|- ( ( ( ph -> ps ) -> ph ) -> ph )