Theorem 19.21bbi

Description: Inference removing two universal quantifiers. Version of 19.21bi with two quantifiers. (Contributed by NM, 20-Apr-1994)

	Ref	Expression
Hypothesis	19.21bbi.1	$$⊢\phi \to \forall x\forall y\psi$$
Assertion	19.21bbi	$$⊢\phi \to \psi$$

Proof

Step	Hyp	Ref	Expression
1		19.21bbi.1	$$⊢\phi \to \forall x\forall y\psi$$
2	1	19.21bi	$$⊢\phi \to \forall y\psi$$
3	2	19.21bi	$$⊢\phi \to \psi$$