Theorem n0ii

Description: If a class has elements, then it is not empty. Inference associated with n0i . (Contributed by BJ, 15-Jul-2021)

	Ref	Expression
Hypothesis	n0ii.1	|- A e. B
Assertion	n0ii	|- -. B = (/)

Proof

Step	Hyp	Ref	Expression
1		n0ii.1	|- A e. B
2		n0i	|- ( A e. B -> -. B = (/) )
3	1 2	ax-mp	|- -. B = (/)