Theorem bj-nfnnfTEMP

Description: New nonfreeness is equivalent to old nonfreeness on core FOL axioms plus sp . (Contributed by BJ, 28-Jul-2023) The proof should not rely on df-nf except via df-nf directly. (Proof modification is discouraged.)

	Ref	Expression
Assertion	bj-nfnnfTEMP	⊢ ( Ⅎ' 𝑥 𝜑 ↔ Ⅎ 𝑥 𝜑 )

Proof

Step	Hyp	Ref	Expression
1		bj-dfnnf3	⊢ ( Ⅎ' 𝑥 𝜑 ↔ ( ∃ 𝑥 𝜑 → ∀ 𝑥 𝜑 ) )
2		df-nf	⊢ ( Ⅎ 𝑥 𝜑 ↔ ( ∃ 𝑥 𝜑 → ∀ 𝑥 𝜑 ) )
3	1 2	bitr4i	⊢ ( Ⅎ' 𝑥 𝜑 ↔ Ⅎ 𝑥 𝜑 )