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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 2449 | . 2 wff ∃𝑥 ∈ 𝐴 𝜑 |
5 | 2 | cv 1347 | . . . . 5 class 𝑥 |
6 | 5, 3 | wcel 2141 | . . . 4 wff 𝑥 ∈ 𝐴 |
7 | 6, 1 | wa 103 | . . 3 wff (𝑥 ∈ 𝐴 ∧ 𝜑) |
8 | 7, 2 | wex 1485 | . 2 wff ∃𝑥(𝑥 ∈ 𝐴 ∧ 𝜑) |
9 | 4, 8 | wb 104 | 1 wff (∃𝑥 ∈ 𝐴 𝜑 ↔ ∃𝑥(𝑥 ∈ 𝐴 ∧ 𝜑)) |
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