| Metamath Proof Explorer | 
      
      
      < Previous  
      Next >
      
       Nearby theorems  | 
  ||
| 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 3051. (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 3420 | . 2 class {𝑥 ∈ 𝐴 ∣ 𝜑} | 
| 5 | 2 | cv 1538 | . . . . 5 class 𝑥 | 
| 6 | 5, 3 | wcel 2107 | . . . 4 wff 𝑥 ∈ 𝐴 | 
| 7 | 6, 1 | wa 395 | . . 3 wff (𝑥 ∈ 𝐴 ∧ 𝜑) | 
| 8 | 7, 2 | cab 2712 | . 2 class {𝑥 ∣ (𝑥 ∈ 𝐴 ∧ 𝜑)} | 
| 9 | 4, 8 | wceq 1539 | 1 wff {𝑥 ∈ 𝐴 ∣ 𝜑} = {𝑥 ∣ (𝑥 ∈ 𝐴 ∧ 𝜑)} | 
| Copyright terms: Public domain | W3C validator |