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| Mirrors > Home > ILE Home > Th. List > df-rex | GIF version | ||
| Description: Define restricted existential quantification. Special case of Definition 4.15(4) of [TakeutiZaring] p. 22. (Contributed by NM, 30-Aug-1993.) | 
| Ref | Expression | 
|---|---|
| df-rex | ⊢ (∃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 | wrex 2476 | . 2 wff ∃𝑥 ∈ 𝐴 𝜑 | 
| 5 | 2 | cv 1363 | . . . . 5 class 𝑥 | 
| 6 | 5, 3 | wcel 2167 | . . . 4 wff 𝑥 ∈ 𝐴 | 
| 7 | 6, 1 | wa 104 | . . 3 wff (𝑥 ∈ 𝐴 ∧ 𝜑) | 
| 8 | 7, 2 | wex 1506 | . 2 wff ∃𝑥(𝑥 ∈ 𝐴 ∧ 𝜑) | 
| 9 | 4, 8 | wb 105 | 1 wff (∃𝑥 ∈ 𝐴 𝜑 ↔ ∃𝑥(𝑥 ∈ 𝐴 ∧ 𝜑)) | 
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