Theorem biorfi

Description: The dual of biorf is not biantr but iba (and ibar ). So there should also be a "biorfr". (Note that these four statements can actually be strengthened to biconditionals.) (Contributed by BJ, 26-Oct-2019)

	Ref	Expression
Hypothesis	biorfi.1	$$⊢\neg \phi$$
Assertion	biorfi	$$⊢\psi \leftrightarrow \left(\phi \vee \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		biorfi.1	$$⊢\neg \phi$$
2		biorf	$$⊢\neg \phi \to \left(\psi \leftrightarrow \left(\phi \vee \psi \right)\right)$$
3	1 2	ax-mp	$$⊢\psi \leftrightarrow \left(\phi \vee \psi \right)$$