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Related theorems GIF version |
| Description: Define restricted existential quantification. Special case of Definition 4.15(4) of [TakeutiZaring] p. 22. |
| Ref | Expression |
|---|---|
| df-rex | ⊢ (∃x ∈ A φ ↔ ∃x(x ∈ A ⋀ φ)) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | wph | . . 3 wff φ | |
| 2 | vx | . . 3 set x | |
| 3 | cA | . . 3 class A | |
| 4 | 1, 2, 3 | wrex 1643 | . 2 wff ∃x ∈ A φ |
| 5 | 2 | cv 953 | . . . . 5 class x |
| 6 | 5, 3 | wcel 956 | . . . 4 wff x ∈ A |
| 7 | 6, 1 | wa 223 | . . 3 wff (x ∈ A ⋀ φ) |
| 8 | 7, 2 | wex 978 | . 2 wff ∃x(x ∈ A ⋀ φ) |
| 9 | 4, 8 | wb 146 | 1 wff (∃x ∈ A φ ↔ ∃x(x ∈ A ⋀ φ)) |