Definition df-in 3906

Description: Define the intersection of two classes. Definition 5.6 of [TakeutiZaring] p. 16. For example, ({1, 3} ∩ {1, 8}) = {1} (ex-in 31005). Contrast this operation with union (𝐴 ∪ 𝐵) (df-un 3904) and difference (𝐴 ∖ 𝐵) (df-dif 3902). For alternate definitions in terms of class difference, requiring no dummy variables, see dfin2 4217 and dfin4 4224. For intersection defined in terms of union, see dfin3 4223. (Contributed by NM, 29-Apr-1994.)

Assertion

Ref	Expression
df-in	⊢ (𝐴 ∩ 𝐵) = {𝑥 ∣ (𝑥 ∈ 𝐴 ∧ 𝑥 ∈ 𝐵)}

Distinct variable groups:   𝑥,𝐴   𝑥,𝐵

Detailed syntax breakdown of Definition df-in

Step	Hyp	Ref	Expression
1		cA	. . 3 class 𝐴
2		cB	. . 3 class 𝐵
3	1, 2	cin 3898	. 2 class (𝐴 ∩ 𝐵)
4		vx	. . . . . 6 setvar 𝑥
5	4	cv 1569	. . . . 5 class 𝑥
6	5, 1	wcel 2145	. . . 4 wff 𝑥 ∈ 𝐴
7	5, 2	wcel 2145	. . . 4 wff 𝑥 ∈ 𝐵
8	6, 7	wa 401	. . 3 wff (𝑥 ∈ 𝐴 ∧ 𝑥 ∈ 𝐵)
9	8, 4	cab 2739	. 2 class {𝑥 ∣ (𝑥 ∈ 𝐴 ∧ 𝑥 ∈ 𝐵)}
10	3, 9	wceq 1570	1 wff (𝐴 ∩ 𝐵) = {𝑥 ∣ (𝑥 ∈ 𝐴 ∧ 𝑥 ∈ 𝐵)}

This definition is used by:  dfin5  3907  elin  3915  dfss2  3917  disj  4403  iinxprg  5049  disjex  33165  disjexc  33166  eulerpartlemt  34983  in-ax8  36980  iocinico  44169  csbingVD  45822