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Mirrors > Home > MPE Home > Th. List > df-rab | Structured version Visualization version GIF version |
Description: Define a restricted class
abstraction (class builder): {𝑥 ∈ 𝐴 ∣ 𝜑}
is the class of all sets 𝑥 in 𝐴 such that 𝜑(𝑥) is true.
Definition of [TakeutiZaring] p.
20.
For the interpretation given in the previous paragraph to be correct, we need to assume Ⅎ𝑥𝐴, which is the case as soon as 𝑥 and 𝐴 are disjoint, which is generally the case. If 𝐴 were to depend on 𝑥, then the interpretation would be less obvious (think of the two extreme cases 𝐴 = {𝑥} and 𝐴 = 𝑥, for instance). See also df-ral 3070. (Contributed by NM, 22-Nov-1994.) |
Ref | Expression |
---|---|
df-rab | ⊢ {𝑥 ∈ 𝐴 ∣ 𝜑} = {𝑥 ∣ (𝑥 ∈ 𝐴 ∧ 𝜑)} |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | wph | . . 3 wff 𝜑 | |
2 | vx | . . 3 setvar 𝑥 | |
3 | cA | . . 3 class 𝐴 | |
4 | 1, 2, 3 | crab 3069 | . 2 class {𝑥 ∈ 𝐴 ∣ 𝜑} |
5 | 2 | cv 1540 | . . . . 5 class 𝑥 |
6 | 5, 3 | wcel 2109 | . . . 4 wff 𝑥 ∈ 𝐴 |
7 | 6, 1 | wa 395 | . . 3 wff (𝑥 ∈ 𝐴 ∧ 𝜑) |
8 | 7, 2 | cab 2716 | . 2 class {𝑥 ∣ (𝑥 ∈ 𝐴 ∧ 𝜑)} |
9 | 4, 8 | wceq 1541 | 1 wff {𝑥 ∈ 𝐴 ∣ 𝜑} = {𝑥 ∣ (𝑥 ∈ 𝐴 ∧ 𝜑)} |
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