Theorem bj-nnfnth

Description: A variable is nonfree in the negation of a theorem, inference form. (Contributed by BJ, 27-Aug-2023)

	Ref	Expression
Hypothesis	bj-nnfnth.1	|- -. ph
Assertion	bj-nnfnth	|- F// x ph

Proof

Step	Hyp	Ref	Expression
1		bj-nnfnth.1	|- -. ph
2	1	bj-nnfth	|- F// x -. ph
3		bj-nnfnt	|- ( F// x ph <-> F// x -. ph )
4	2 3	mpbir	|- F// x ph