Definition df-dm 5686

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 29682). Another example is the domain of the complex arctangent, (𝐴 ∈ dom arctan ↔ (𝐴 ∈ ℂ ∧ 𝐴 ≠ -i ∧ 𝐴 ≠ i)) (for proof see atandm 26371). Contrast with range (defined in df-rn 5687). For alternate definitions see dfdm2 6278, dfdm3 5886, and dfdm4 5894. 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 5676	. 2 class dom 𝐴
3		vx	. . . . . 6 setvar 𝑥
4	3	cv 1541	. . . . 5 class 𝑥
5		vy	. . . . . 6 setvar 𝑦
6	5	cv 1541	. . . . 5 class 𝑦
7	4, 6, 1	wbr 5148	. . . 4 wff 𝑥𝐴𝑦
8	7, 5	wex 1782	. . 3 wff ∃𝑦 𝑥𝐴𝑦
9	8, 3	cab 2710	. 2 class {𝑥 ∣ ∃𝑦 𝑥𝐴𝑦}
10	2, 9	wceq 1542	1 wff dom 𝐴 = {𝑥 ∣ ∃𝑦 𝑥𝐴𝑦}

This definition is referenced by:  dfdm3  5886  dfrn2  5887  dfdm4  5894  dfdmf  5895  eldmg  5897  dmun  5909  dm0rn0  5923  nfdm  5949  fliftf  7309  opabdm  31828  rncossdmcoss  37314  dfatco  45951