Definition df-dm 5546

Description: Define the domain of a class. Definition 3 of [Suppes] p. 59. For example, 𝐹 = {⟨2, 6⟩, ⟨3, 9⟩} → dom 𝐹 = {2, 3} (ex-dm 28476). Another example is the domain of the complex arctangent, (𝐴 ∈ dom arctan ↔ (𝐴 ∈ ℂ ∧ 𝐴 ≠ -i ∧ 𝐴 ≠ i)) (for proof see atandm 25713). Contrast with range (defined in df-rn 5547). For alternate definitions see dfdm2 6124, dfdm3 5741, and dfdm4 5749. The notation "dom " is used by Enderton; other authors sometimes use script D. (Contributed by NM, 1-Aug-1994.)

Assertion

Ref	Expression
df-dm	⊢ dom 𝐴 = {𝑥 ∣ ∃𝑦 𝑥𝐴𝑦}

Distinct variable group:   𝑥,𝑦,𝐴

Detailed syntax breakdown of Definition df-dm

Step	Hyp	Ref	Expression
1		cA	. . 3 class 𝐴
2	1	cdm 5536	. 2 class dom 𝐴
3		vx	. . . . . 6 setvar 𝑥
4	3	cv 1542	. . . . 5 class 𝑥
5		vy	. . . . . 6 setvar 𝑦
6	5	cv 1542	. . . . 5 class 𝑦
7	4, 6, 1	wbr 5039	. . . 4 wff 𝑥𝐴𝑦
8	7, 5	wex 1787	. . 3 wff ∃𝑦 𝑥𝐴𝑦
9	8, 3	cab 2714	. 2 class {𝑥 ∣ ∃𝑦 𝑥𝐴𝑦}
10	2, 9	wceq 1543	1 wff dom 𝐴 = {𝑥 ∣ ∃𝑦 𝑥𝐴𝑦}

This definition is referenced by:  dfdm3  5741  dfrn2  5742  dfdm4  5749  dfdmf  5750  eldmg  5752  dmun  5764  domepOLD  5778  dm0rn0  5779  nfdm  5805  fliftf  7102  opabdm  30624  rncossdmcoss  36259  dfatco  44363