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 𝑥𝐴 𝐵

Proof

Step Hyp Ref Expression
1 df-iun 𝑥𝐴 𝐵 = { 𝑦 ∣ ∃ 𝑥𝐴 𝑦𝐵 }
2 nfre1 𝑥𝑥𝐴 𝑦𝐵
3 2 nfab 𝑥 { 𝑦 ∣ ∃ 𝑥𝐴 𝑦𝐵 }
4 1 3 nfcxfr 𝑥 𝑥𝐴 𝐵