| Step | Hyp | Ref
| Expression |
| 1 | | idn3 44635 |
. . . . . . . . . . . . . 14
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , ((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ∧ 𝑧 ∈ (𝑎 ∩ 𝑦)) ▶ ((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ∧ 𝑧 ∈ (𝑎 ∩ 𝑦)) ) |
| 2 | | simpr 484 |
. . . . . . . . . . . . . 14
⊢ (((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ∧ 𝑧 ∈ (𝑎 ∩ 𝑦)) → 𝑧 ∈ (𝑎 ∩ 𝑦)) |
| 3 | 1, 2 | e3 44757 |
. . . . . . . . . . . . 13
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , ((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ∧ 𝑧 ∈ (𝑎 ∩ 𝑦)) ▶ 𝑧 ∈ (𝑎 ∩ 𝑦) ) |
| 4 | | inss2 4238 |
. . . . . . . . . . . . . 14
⊢ (𝑎 ∩ 𝑦) ⊆ 𝑦 |
| 5 | 4 | sseli 3979 |
. . . . . . . . . . . . 13
⊢ (𝑧 ∈ (𝑎 ∩ 𝑦) → 𝑧 ∈ 𝑦) |
| 6 | 3, 5 | e3 44757 |
. . . . . . . . . . . 12
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , ((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ∧ 𝑧 ∈ (𝑎 ∩ 𝑦)) ▶ 𝑧 ∈ 𝑦 ) |
| 7 | | inss1 4237 |
. . . . . . . . . . . . . . 15
⊢ (𝑎 ∩ 𝑦) ⊆ 𝑎 |
| 8 | 7 | sseli 3979 |
. . . . . . . . . . . . . 14
⊢ (𝑧 ∈ (𝑎 ∩ 𝑦) → 𝑧 ∈ 𝑎) |
| 9 | 3, 8 | e3 44757 |
. . . . . . . . . . . . 13
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , ((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ∧ 𝑧 ∈ (𝑎 ∩ 𝑦)) ▶ 𝑧 ∈ 𝑎 ) |
| 10 | | idn2 44633 |
. . . . . . . . . . . . . . . . . 18
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) ▶ (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) ) |
| 11 | | simpl 482 |
. . . . . . . . . . . . . . . . . 18
⊢ ((𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) → 𝑥 ∈ 𝑎) |
| 12 | 10, 11 | e2 44651 |
. . . . . . . . . . . . . . . . 17
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) ▶ 𝑥 ∈ 𝑎 ) |
| 13 | | idn1 44594 |
. . . . . . . . . . . . . . . . . 18
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) ▶ (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) ) |
| 14 | | simpl 482 |
. . . . . . . . . . . . . . . . . 18
⊢ ((𝑎 ⊆ On ∧ 𝑎 ≠ ∅) → 𝑎 ⊆ On) |
| 15 | 13, 14 | e1a 44647 |
. . . . . . . . . . . . . . . . 17
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) ▶ 𝑎 ⊆ On ) |
| 16 | | ssel 3977 |
. . . . . . . . . . . . . . . . . 18
⊢ (𝑎 ⊆ On → (𝑥 ∈ 𝑎 → 𝑥 ∈ On)) |
| 17 | 16 | com12 32 |
. . . . . . . . . . . . . . . . 17
⊢ (𝑥 ∈ 𝑎 → (𝑎 ⊆ On → 𝑥 ∈ On)) |
| 18 | 12, 15, 17 | e21 44750 |
. . . . . . . . . . . . . . . 16
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) ▶ 𝑥 ∈ On ) |
| 19 | | eloni 6394 |
. . . . . . . . . . . . . . . 16
⊢ (𝑥 ∈ On → Ord 𝑥) |
| 20 | 18, 19 | e2 44651 |
. . . . . . . . . . . . . . 15
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) ▶ Ord 𝑥 ) |
| 21 | | ordtr 6398 |
. . . . . . . . . . . . . . 15
⊢ (Ord
𝑥 → Tr 𝑥) |
| 22 | 20, 21 | e2 44651 |
. . . . . . . . . . . . . 14
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) ▶ Tr 𝑥 ) |
| 23 | | simpll 767 |
. . . . . . . . . . . . . . . 16
⊢ (((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ∧ 𝑧 ∈ (𝑎 ∩ 𝑦)) → 𝑦 ∈ (𝑎 ∩ 𝑥)) |
| 24 | 1, 23 | e3 44757 |
. . . . . . . . . . . . . . 15
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , ((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ∧ 𝑧 ∈ (𝑎 ∩ 𝑦)) ▶ 𝑦 ∈ (𝑎 ∩ 𝑥) ) |
| 25 | | inss2 4238 |
. . . . . . . . . . . . . . . 16
⊢ (𝑎 ∩ 𝑥) ⊆ 𝑥 |
| 26 | 25 | sseli 3979 |
. . . . . . . . . . . . . . 15
⊢ (𝑦 ∈ (𝑎 ∩ 𝑥) → 𝑦 ∈ 𝑥) |
| 27 | 24, 26 | e3 44757 |
. . . . . . . . . . . . . 14
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , ((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ∧ 𝑧 ∈ (𝑎 ∩ 𝑦)) ▶ 𝑦 ∈ 𝑥 ) |
| 28 | | trel 5268 |
. . . . . . . . . . . . . . 15
⊢ (Tr 𝑥 → ((𝑧 ∈ 𝑦 ∧ 𝑦 ∈ 𝑥) → 𝑧 ∈ 𝑥)) |
| 29 | 28 | expcomd 416 |
. . . . . . . . . . . . . 14
⊢ (Tr 𝑥 → (𝑦 ∈ 𝑥 → (𝑧 ∈ 𝑦 → 𝑧 ∈ 𝑥))) |
| 30 | 22, 27, 6, 29 | e233 44785 |
. . . . . . . . . . . . 13
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , ((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ∧ 𝑧 ∈ (𝑎 ∩ 𝑦)) ▶ 𝑧 ∈ 𝑥 ) |
| 31 | | elin 3967 |
. . . . . . . . . . . . . 14
⊢ (𝑧 ∈ (𝑎 ∩ 𝑥) ↔ (𝑧 ∈ 𝑎 ∧ 𝑧 ∈ 𝑥)) |
| 32 | 31 | simplbi2 500 |
. . . . . . . . . . . . 13
⊢ (𝑧 ∈ 𝑎 → (𝑧 ∈ 𝑥 → 𝑧 ∈ (𝑎 ∩ 𝑥))) |
| 33 | 9, 30, 32 | e33 44754 |
. . . . . . . . . . . 12
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , ((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ∧ 𝑧 ∈ (𝑎 ∩ 𝑦)) ▶ 𝑧 ∈ (𝑎 ∩ 𝑥) ) |
| 34 | | elin 3967 |
. . . . . . . . . . . . 13
⊢ (𝑧 ∈ ((𝑎 ∩ 𝑥) ∩ 𝑦) ↔ (𝑧 ∈ (𝑎 ∩ 𝑥) ∧ 𝑧 ∈ 𝑦)) |
| 35 | 34 | simplbi2com 502 |
. . . . . . . . . . . 12
⊢ (𝑧 ∈ 𝑦 → (𝑧 ∈ (𝑎 ∩ 𝑥) → 𝑧 ∈ ((𝑎 ∩ 𝑥) ∩ 𝑦))) |
| 36 | 6, 33, 35 | e33 44754 |
. . . . . . . . . . 11
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , ((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ∧ 𝑧 ∈ (𝑎 ∩ 𝑦)) ▶ 𝑧 ∈ ((𝑎 ∩ 𝑥) ∩ 𝑦) ) |
| 37 | 36 | in3an 44631 |
. . . . . . . . . 10
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , (𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ▶ (𝑧 ∈ (𝑎 ∩ 𝑦) → 𝑧 ∈ ((𝑎 ∩ 𝑥) ∩ 𝑦)) ) |
| 38 | 37 | gen31 44641 |
. . . . . . . . 9
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , (𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ▶ ∀𝑧(𝑧 ∈ (𝑎 ∩ 𝑦) → 𝑧 ∈ ((𝑎 ∩ 𝑥) ∩ 𝑦)) ) |
| 39 | | df-ss 3968 |
. . . . . . . . . 10
⊢ ((𝑎 ∩ 𝑦) ⊆ ((𝑎 ∩ 𝑥) ∩ 𝑦) ↔ ∀𝑧(𝑧 ∈ (𝑎 ∩ 𝑦) → 𝑧 ∈ ((𝑎 ∩ 𝑥) ∩ 𝑦))) |
| 40 | 39 | biimpri 228 |
. . . . . . . . 9
⊢
(∀𝑧(𝑧 ∈ (𝑎 ∩ 𝑦) → 𝑧 ∈ ((𝑎 ∩ 𝑥) ∩ 𝑦)) → (𝑎 ∩ 𝑦) ⊆ ((𝑎 ∩ 𝑥) ∩ 𝑦)) |
| 41 | 38, 40 | e3 44757 |
. . . . . . . 8
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , (𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ▶ (𝑎 ∩ 𝑦) ⊆ ((𝑎 ∩ 𝑥) ∩ 𝑦) ) |
| 42 | | idn3 44635 |
. . . . . . . . 9
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , (𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ▶ (𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ) |
| 43 | | simpr 484 |
. . . . . . . . 9
⊢ ((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) → ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) |
| 44 | 42, 43 | e3 44757 |
. . . . . . . 8
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , (𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ▶ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅ ) |
| 45 | | sseq0 4403 |
. . . . . . . . 9
⊢ (((𝑎 ∩ 𝑦) ⊆ ((𝑎 ∩ 𝑥) ∩ 𝑦) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) → (𝑎 ∩ 𝑦) = ∅) |
| 46 | 45 | ex 412 |
. . . . . . . 8
⊢ ((𝑎 ∩ 𝑦) ⊆ ((𝑎 ∩ 𝑥) ∩ 𝑦) → (((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅ → (𝑎 ∩ 𝑦) = ∅)) |
| 47 | 41, 44, 46 | e33 44754 |
. . . . . . 7
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , (𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ▶ (𝑎 ∩ 𝑦) = ∅ ) |
| 48 | | simpl 482 |
. . . . . . . . 9
⊢ ((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) → 𝑦 ∈ (𝑎 ∩ 𝑥)) |
| 49 | 42, 48 | e3 44757 |
. . . . . . . 8
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , (𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ▶ 𝑦 ∈ (𝑎 ∩ 𝑥) ) |
| 50 | | inss1 4237 |
. . . . . . . . 9
⊢ (𝑎 ∩ 𝑥) ⊆ 𝑎 |
| 51 | 50 | sseli 3979 |
. . . . . . . 8
⊢ (𝑦 ∈ (𝑎 ∩ 𝑥) → 𝑦 ∈ 𝑎) |
| 52 | 49, 51 | e3 44757 |
. . . . . . 7
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , (𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ▶ 𝑦 ∈ 𝑎 ) |
| 53 | | pm3.21 471 |
. . . . . . 7
⊢ ((𝑎 ∩ 𝑦) = ∅ → (𝑦 ∈ 𝑎 → (𝑦 ∈ 𝑎 ∧ (𝑎 ∩ 𝑦) = ∅))) |
| 54 | 47, 52, 53 | e33 44754 |
. . . . . 6
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) , (𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ▶ (𝑦 ∈ 𝑎 ∧ (𝑎 ∩ 𝑦) = ∅) ) |
| 55 | 54 | in3 44629 |
. . . . 5
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) ▶ ((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) → (𝑦 ∈ 𝑎 ∧ (𝑎 ∩ 𝑦) = ∅)) ) |
| 56 | 55 | gen21 44639 |
. . . 4
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) ▶ ∀𝑦((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) → (𝑦 ∈ 𝑎 ∧ (𝑎 ∩ 𝑦) = ∅)) ) |
| 57 | | exim 1834 |
. . . 4
⊢
(∀𝑦((𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) → (𝑦 ∈ 𝑎 ∧ (𝑎 ∩ 𝑦) = ∅)) → (∃𝑦(𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) → ∃𝑦(𝑦 ∈ 𝑎 ∧ (𝑎 ∩ 𝑦) = ∅))) |
| 58 | 56, 57 | e2 44651 |
. . 3
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) ▶ (∃𝑦(𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) → ∃𝑦(𝑦 ∈ 𝑎 ∧ (𝑎 ∩ 𝑦) = ∅)) ) |
| 59 | | onfrALTlem3VD 44907 |
. . . 4
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) ▶ ∃𝑦 ∈ (𝑎 ∩ 𝑥)((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅ ) |
| 60 | | df-rex 3071 |
. . . . 5
⊢
(∃𝑦 ∈
(𝑎 ∩ 𝑥)((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅ ↔ ∃𝑦(𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅)) |
| 61 | 60 | biimpi 216 |
. . . 4
⊢
(∃𝑦 ∈
(𝑎 ∩ 𝑥)((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅ → ∃𝑦(𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅)) |
| 62 | 59, 61 | e2 44651 |
. . 3
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) ▶ ∃𝑦(𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) ) |
| 63 | | id 22 |
. . 3
⊢
((∃𝑦(𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) → ∃𝑦(𝑦 ∈ 𝑎 ∧ (𝑎 ∩ 𝑦) = ∅)) → (∃𝑦(𝑦 ∈ (𝑎 ∩ 𝑥) ∧ ((𝑎 ∩ 𝑥) ∩ 𝑦) = ∅) → ∃𝑦(𝑦 ∈ 𝑎 ∧ (𝑎 ∩ 𝑦) = ∅))) |
| 64 | 58, 62, 63 | e22 44691 |
. 2
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) ▶ ∃𝑦(𝑦 ∈ 𝑎 ∧ (𝑎 ∩ 𝑦) = ∅) ) |
| 65 | | df-rex 3071 |
. . 3
⊢
(∃𝑦 ∈
𝑎 (𝑎 ∩ 𝑦) = ∅ ↔ ∃𝑦(𝑦 ∈ 𝑎 ∧ (𝑎 ∩ 𝑦) = ∅)) |
| 66 | 65 | biimpri 228 |
. 2
⊢
(∃𝑦(𝑦 ∈ 𝑎 ∧ (𝑎 ∩ 𝑦) = ∅) → ∃𝑦 ∈ 𝑎 (𝑎 ∩ 𝑦) = ∅) |
| 67 | 64, 66 | e2 44651 |
1
⊢ ( (𝑎 ⊆ On ∧ 𝑎 ≠ ∅) , (𝑥 ∈ 𝑎 ∧ ¬ (𝑎 ∩ 𝑥) = ∅) ▶ ∃𝑦 ∈ 𝑎 (𝑎 ∩ 𝑦) = ∅ ) |