Metamath Proof Explorer


Theorem nfun

Description: Bound-variable hypothesis builder for the union of classes. (Contributed by NM, 15-Sep-2003) (Revised by Mario Carneiro, 14-Oct-2016) Avoid ax-10 , ax-11 , ax-12 . (Revised by SN, 14-May-2025)

Ref Expression
Hypotheses nfun.1 _ x A
nfun.2 _ x B
Assertion nfun _ x A B

Proof

Step Hyp Ref Expression
1 nfun.1 _ x A
2 nfun.2 _ x B
3 elun y A B y A y B
4 1 nfcri x y A
5 2 nfcri x y B
6 4 5 nfor x y A y B
7 3 6 nfxfr x y A B
8 7 nfci _ x A B