Theorem bj-nfeel2

Description: Nonfreeness in a membership statement. (Contributed by BJ, 20-Oct-2021) (Proof modification is discouraged.)

	Ref	Expression
Assertion	bj-nfeel2	$$⊢\neg \forall xx=y\to Ⅎxy\in z$$

Proof

Step	Hyp	Ref	Expression
1		nfv	$$⊢Ⅎxt\in z$$
2		elequ1	$$⊢t=y\to \left(t\in z\leftrightarrow y\in z\right)$$
3	1 2	bj-dvelimv	$$⊢\neg \forall xx=y\to Ⅎxy\in z$$