Theorem bj-nnftht

Description: A variable is nonfree in a theorem. The antecedent is in the "strong necessity" modality of modal logic in order not to require sp (modal T), as in bj-nnfbi . (Contributed by BJ, 28-Jul-2023)

	Ref	Expression
Assertion	bj-nnftht	|- ( ( ph /\ A. x ph ) -> F// x ph )

Proof

Step	Hyp	Ref	Expression
1		bj-alnnf2	|- ( ph -> ( A. x ph <-> F// x ph ) )
2	1	biimpa	|- ( ( ph /\ A. x ph ) -> F// x ph )