Definition df-un 3161

Description: Define the union of two classes. Definition 5.6 of [TakeutiZaring] p. 16. Contrast this operation with difference (𝐴 ∖ 𝐵) (df-dif 3159) and intersection (𝐴 ∩ 𝐵) (df-in 3163). (Contributed by NM, 23-Aug-1993.)

Assertion

Ref	Expression
df-un	⊢ (𝐴 ∪ 𝐵) = {𝑥 ∣ (𝑥 ∈ 𝐴 ∨ 𝑥 ∈ 𝐵)}

Distinct variable groups:   𝑥,𝐴   𝑥,𝐵

Detailed syntax breakdown of Definition df-un

Step	Hyp	Ref	Expression
1		cA	. . 3 class 𝐴
2		cB	. . 3 class 𝐵
3	1, 2	cun 3155	. 2 class (𝐴 ∪ 𝐵)
4		vx	. . . . . 6 setvar 𝑥
5	4	cv 1363	. . . . 5 class 𝑥
6	5, 1	wcel 2167	. . . 4 wff 𝑥 ∈ 𝐴
7	5, 2	wcel 2167	. . . 4 wff 𝑥 ∈ 𝐵
8	6, 7	wo 709	. . 3 wff (𝑥 ∈ 𝐴 ∨ 𝑥 ∈ 𝐵)
9	8, 4	cab 2182	. 2 class {𝑥 ∣ (𝑥 ∈ 𝐴 ∨ 𝑥 ∈ 𝐵)}
10	3, 9	wceq 1364	1 wff (𝐴 ∪ 𝐵) = {𝑥 ∣ (𝑥 ∈ 𝐴 ∨ 𝑥 ∈ 𝐵)}

This definition is referenced by:  elun  3304  nfun  3319  unipr  3853  iinuniss  3999  bdcun  15508