Metamath Proof Explorer


Theorem nfiu1OLD

Description: Obsolete version of nfiu1 as of 14-May-2025. (Contributed by NM, 12-Oct-2003) (Proof modification is discouraged.) (New usage is discouraged.)

Ref Expression
Assertion nfiu1OLD _ x x A B

Proof

Step Hyp Ref Expression
1 df-iun x A B = y | x A y B
2 nfre1 x x A y B
3 2 nfab _ x y | x A y B
4 1 3 nfcxfr _ x x A B