Theorem elnotel

Description: A class cannot be an element of one of its elements. (Contributed by AV, 14-Jun-2022)

	Ref	Expression
Assertion	elnotel	$$⊢A\in B\to \neg B\in A$$

Proof

Step	Hyp	Ref	Expression
1		en2lp	$$⊢\neg \left(A\in B\wedge B\in A\right)$$
2	1	imnani	$$⊢A\in B\to \neg B\in A$$