Theorem nfiundg

Description: Bound-variable hypothesis builder for indexed union. Usage of this theorem is discouraged because it depends on ax-13 , see nfiund for a weaker version that does not require it. (Contributed by Emmett Weisz, 6-Dec-2019) (New usage is discouraged.)

	Ref	Expression
Hypotheses	nfiundg.1	⊢ Ⅎ 𝑥 𝜑
	nfiundg.2	⊢ ( 𝜑 → Ⅎ 𝑦 𝐴 )
	nfiundg.3	⊢ ( 𝜑 → Ⅎ 𝑦 𝐵 )
Assertion	nfiundg	⊢ ( 𝜑 → Ⅎ 𝑦 ∪ 𝑥 ∈ 𝐴 𝐵 )

Proof

Step	Hyp	Ref	Expression
1		nfiundg.1	⊢ Ⅎ 𝑥 𝜑
2		nfiundg.2	⊢ ( 𝜑 → Ⅎ 𝑦 𝐴 )
3		nfiundg.3	⊢ ( 𝜑 → Ⅎ 𝑦 𝐵 )
4		df-iun	⊢ ∪ 𝑥 ∈ 𝐴 𝐵 = { 𝑧 ∣ ∃ 𝑥 ∈ 𝐴 𝑧 ∈ 𝐵 }
5		nfv	⊢ Ⅎ 𝑧 𝜑
6	3	nfcrd	⊢ ( 𝜑 → Ⅎ 𝑦 𝑧 ∈ 𝐵 )
7	1 2 6	nfrexdg	⊢ ( 𝜑 → Ⅎ 𝑦 ∃ 𝑥 ∈ 𝐴 𝑧 ∈ 𝐵 )
8	5 7	nfabd	⊢ ( 𝜑 → Ⅎ 𝑦 { 𝑧 ∣ ∃ 𝑥 ∈ 𝐴 𝑧 ∈ 𝐵 } )
9	4 8	nfcxfrd	⊢ ( 𝜑 → Ⅎ 𝑦 ∪ 𝑥 ∈ 𝐴 𝐵 )