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Mirrors > Home > MPE Home > Th. List > df-dm | Structured version Visualization version GIF version |
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 30187). Another example is the domain of the complex arctangent, (𝐴 ∈ dom arctan ↔ (𝐴 ∈ ℂ ∧ 𝐴 ≠ -i ∧ 𝐴 ≠ i)) (for proof see atandm 26749). Contrast with range (defined in df-rn 5678). For alternate definitions see dfdm2 6271, dfdm3 5878, and dfdm4 5886. The notation "dom " is used by Enderton; other authors sometimes use script D. (Contributed by NM, 1-Aug-1994.) |
Ref | Expression |
---|---|
df-dm | ⊢ dom 𝐴 = {𝑥 ∣ ∃𝑦 𝑥𝐴𝑦} |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | cA | . . 3 class 𝐴 | |
2 | 1 | cdm 5667 | . 2 class dom 𝐴 |
3 | vx | . . . . . 6 setvar 𝑥 | |
4 | 3 | cv 1532 | . . . . 5 class 𝑥 |
5 | vy | . . . . . 6 setvar 𝑦 | |
6 | 5 | cv 1532 | . . . . 5 class 𝑦 |
7 | 4, 6, 1 | wbr 5139 | . . . 4 wff 𝑥𝐴𝑦 |
8 | 7, 5 | wex 1773 | . . 3 wff ∃𝑦 𝑥𝐴𝑦 |
9 | 8, 3 | cab 2701 | . 2 class {𝑥 ∣ ∃𝑦 𝑥𝐴𝑦} |
10 | 2, 9 | wceq 1533 | 1 wff dom 𝐴 = {𝑥 ∣ ∃𝑦 𝑥𝐴𝑦} |
Colors of variables: wff setvar class |
This definition is referenced by: dfdm3 5878 dfrn2 5879 dfdm4 5886 dfdmf 5887 eldmg 5889 dmun 5901 dm0rn0 5915 nfdm 5941 fliftf 7305 opabdm 32335 rncossdmcoss 37829 dfatco 46510 |
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