Theorem 2albii

Description: Inference adding two universal quantifiers to both sides of an equivalence. (Contributed by NM, 9-Mar-1997)

	Ref	Expression
Hypothesis	albii.1	$$⊢\phi \leftrightarrow \psi$$
Assertion	2albii	$$⊢\forall x\forall y\phi \leftrightarrow \forall x\forall y\psi$$

Proof

Step	Hyp	Ref	Expression
1		albii.1	$$⊢\phi \leftrightarrow \psi$$
2	1	albii	$$⊢\forall y\phi \leftrightarrow \forall y\psi$$
3	2	albii	$$⊢\forall x\forall y\phi \leftrightarrow \forall x\forall y\psi$$