Theorem nex

Description: Generalization rule for negated wff. (Contributed by NM, 18-May-1994)

	Ref	Expression
Hypothesis	nex.1	|- -. ph
Assertion	nex	|- -. E. x ph

Proof

Step	Hyp	Ref	Expression
1		nex.1	|- -. ph
2		alnex	|- ( A. x -. ph <-> -. E. x ph )
3	2 1	mpgbi	|- -. E. x ph