Theorem pm5.5

Description: Theorem *5.5 of WhiteheadRussell p. 125. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm5.5	$$⊢\phi \to \left(\left(\phi \to \psi \right)\leftrightarrow \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		biimt	$$⊢\phi \to \left(\psi \leftrightarrow \left(\phi \to \psi \right)\right)$$
2	1	bicomd	$$⊢\phi \to \left(\left(\phi \to \psi \right)\leftrightarrow \psi \right)$$