Step | Hyp | Ref
| Expression |
1 | | elex 3459 |
. 2
⊢ (𝐴 ∈ (𝐵 ∪ 𝐶) → 𝐴 ∈ V) |
2 | | elex 3459 |
. . 3
⊢ (𝐴 ∈ 𝐵 → 𝐴 ∈ V) |
3 | | elex 3459 |
. . 3
⊢ (𝐴 ∈ 𝐶 → 𝐴 ∈ V) |
4 | 2, 3 | jaoi 854 |
. 2
⊢ ((𝐴 ∈ 𝐵 ∨ 𝐴 ∈ 𝐶) → 𝐴 ∈ V) |
5 | | eleq1 2877 |
. . . 4
⊢ (𝑥 = 𝑦 → (𝑥 ∈ 𝐵 ↔ 𝑦 ∈ 𝐵)) |
6 | | eleq1 2877 |
. . . 4
⊢ (𝑥 = 𝑦 → (𝑥 ∈ 𝐶 ↔ 𝑦 ∈ 𝐶)) |
7 | 5, 6 | orbi12d 916 |
. . 3
⊢ (𝑥 = 𝑦 → ((𝑥 ∈ 𝐵 ∨ 𝑥 ∈ 𝐶) ↔ (𝑦 ∈ 𝐵 ∨ 𝑦 ∈ 𝐶))) |
8 | | eleq1 2877 |
. . . 4
⊢ (𝑦 = 𝐴 → (𝑦 ∈ 𝐵 ↔ 𝐴 ∈ 𝐵)) |
9 | | eleq1 2877 |
. . . 4
⊢ (𝑦 = 𝐴 → (𝑦 ∈ 𝐶 ↔ 𝐴 ∈ 𝐶)) |
10 | 8, 9 | orbi12d 916 |
. . 3
⊢ (𝑦 = 𝐴 → ((𝑦 ∈ 𝐵 ∨ 𝑦 ∈ 𝐶) ↔ (𝐴 ∈ 𝐵 ∨ 𝐴 ∈ 𝐶))) |
11 | | df-un 3886 |
. . 3
⊢ (𝐵 ∪ 𝐶) = {𝑥 ∣ (𝑥 ∈ 𝐵 ∨ 𝑥 ∈ 𝐶)} |
12 | 7, 10, 11 | elab2gw 3613 |
. 2
⊢ (𝐴 ∈ V → (𝐴 ∈ (𝐵 ∪ 𝐶) ↔ (𝐴 ∈ 𝐵 ∨ 𝐴 ∈ 𝐶))) |
13 | 1, 4, 12 | pm5.21nii 383 |
1
⊢ (𝐴 ∈ (𝐵 ∪ 𝐶) ↔ (𝐴 ∈ 𝐵 ∨ 𝐴 ∈ 𝐶)) |