Theorem difidALT

Description: Alternate proof of difid . (Contributed by David Abernethy, 17-Jun-2012) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	difidALT	|- ( A \ A ) = (/)

Proof

Step	Hyp	Ref	Expression
1		dfdif2	|- ( A \ A ) = { x e. A | -. x e. A }
2		dfnul3	|- (/) = { x e. A | -. x e. A }
3	1 2	eqtr4i	|- ( A \ A ) = (/)