| Step | Hyp | Ref
 | Expression | 
| 1 |   | noel 3454 | 
. 2
⊢  ¬
∅ ∈ ∅ | 
| 2 |   | df-suc 4406 | 
. . . . . 6
⊢ suc 𝑦 = (𝑦 ∪ {𝑦}) | 
| 3 | 2 | eleq2i 2263 | 
. . . . 5
⊢ (suc
𝑦 ∈ suc 𝑦 ↔ suc 𝑦 ∈ (𝑦 ∪ {𝑦})) | 
| 4 |   | elun 3304 | 
. . . . . 6
⊢ (suc
𝑦 ∈ (𝑦 ∪ {𝑦}) ↔ (suc 𝑦 ∈ 𝑦 ∨ suc 𝑦 ∈ {𝑦})) | 
| 5 |   | bj-nntrans 15597 | 
. . . . . . . 8
⊢ (𝑦 ∈ ω → (suc
𝑦 ∈ 𝑦 → suc 𝑦 ⊆ 𝑦)) | 
| 6 |   | sucssel 4459 | 
. . . . . . . 8
⊢ (𝑦 ∈ ω → (suc
𝑦 ⊆ 𝑦 → 𝑦 ∈ 𝑦)) | 
| 7 | 5, 6 | syld 45 | 
. . . . . . 7
⊢ (𝑦 ∈ ω → (suc
𝑦 ∈ 𝑦 → 𝑦 ∈ 𝑦)) | 
| 8 |   | vex 2766 | 
. . . . . . . . . 10
⊢ 𝑦 ∈ V | 
| 9 | 8 | sucid 4452 | 
. . . . . . . . 9
⊢ 𝑦 ∈ suc 𝑦 | 
| 10 |   | elsni 3640 | 
. . . . . . . . 9
⊢ (suc
𝑦 ∈ {𝑦} → suc 𝑦 = 𝑦) | 
| 11 | 9, 10 | eleqtrid 2285 | 
. . . . . . . 8
⊢ (suc
𝑦 ∈ {𝑦} → 𝑦 ∈ 𝑦) | 
| 12 | 11 | a1i 9 | 
. . . . . . 7
⊢ (𝑦 ∈ ω → (suc
𝑦 ∈ {𝑦} → 𝑦 ∈ 𝑦)) | 
| 13 | 7, 12 | jaod 718 | 
. . . . . 6
⊢ (𝑦 ∈ ω → ((suc
𝑦 ∈ 𝑦 ∨ suc 𝑦 ∈ {𝑦}) → 𝑦 ∈ 𝑦)) | 
| 14 | 4, 13 | biimtrid 152 | 
. . . . 5
⊢ (𝑦 ∈ ω → (suc
𝑦 ∈ (𝑦 ∪ {𝑦}) → 𝑦 ∈ 𝑦)) | 
| 15 | 3, 14 | biimtrid 152 | 
. . . 4
⊢ (𝑦 ∈ ω → (suc
𝑦 ∈ suc 𝑦 → 𝑦 ∈ 𝑦)) | 
| 16 | 15 | con3d 632 | 
. . 3
⊢ (𝑦 ∈ ω → (¬
𝑦 ∈ 𝑦 → ¬ suc 𝑦 ∈ suc 𝑦)) | 
| 17 | 16 | rgen 2550 | 
. 2
⊢
∀𝑦 ∈
ω (¬ 𝑦 ∈
𝑦 → ¬ suc 𝑦 ∈ suc 𝑦) | 
| 18 |   | ax-bdel 15467 | 
. . . 4
⊢
BOUNDED 𝑥 ∈ 𝑥 | 
| 19 | 18 | ax-bdn 15463 | 
. . 3
⊢
BOUNDED ¬ 𝑥 ∈ 𝑥 | 
| 20 |   | nfv 1542 | 
. . 3
⊢
Ⅎ𝑥 ¬
∅ ∈ ∅ | 
| 21 |   | nfv 1542 | 
. . 3
⊢
Ⅎ𝑥 ¬ 𝑦 ∈ 𝑦 | 
| 22 |   | nfv 1542 | 
. . 3
⊢
Ⅎ𝑥 ¬ suc
𝑦 ∈ suc 𝑦 | 
| 23 |   | eleq1 2259 | 
. . . . . 6
⊢ (𝑥 = ∅ → (𝑥 ∈ 𝑥 ↔ ∅ ∈ 𝑥)) | 
| 24 |   | eleq2 2260 | 
. . . . . 6
⊢ (𝑥 = ∅ → (∅
∈ 𝑥 ↔ ∅
∈ ∅)) | 
| 25 | 23, 24 | bitrd 188 | 
. . . . 5
⊢ (𝑥 = ∅ → (𝑥 ∈ 𝑥 ↔ ∅ ∈
∅)) | 
| 26 | 25 | notbid 668 | 
. . . 4
⊢ (𝑥 = ∅ → (¬ 𝑥 ∈ 𝑥 ↔ ¬ ∅ ∈
∅)) | 
| 27 | 26 | biimprd 158 | 
. . 3
⊢ (𝑥 = ∅ → (¬ ∅
∈ ∅ → ¬ 𝑥 ∈ 𝑥)) | 
| 28 |   | elequ1 2171 | 
. . . . . 6
⊢ (𝑥 = 𝑦 → (𝑥 ∈ 𝑥 ↔ 𝑦 ∈ 𝑥)) | 
| 29 |   | elequ2 2172 | 
. . . . . 6
⊢ (𝑥 = 𝑦 → (𝑦 ∈ 𝑥 ↔ 𝑦 ∈ 𝑦)) | 
| 30 | 28, 29 | bitrd 188 | 
. . . . 5
⊢ (𝑥 = 𝑦 → (𝑥 ∈ 𝑥 ↔ 𝑦 ∈ 𝑦)) | 
| 31 | 30 | notbid 668 | 
. . . 4
⊢ (𝑥 = 𝑦 → (¬ 𝑥 ∈ 𝑥 ↔ ¬ 𝑦 ∈ 𝑦)) | 
| 32 | 31 | biimpd 144 | 
. . 3
⊢ (𝑥 = 𝑦 → (¬ 𝑥 ∈ 𝑥 → ¬ 𝑦 ∈ 𝑦)) | 
| 33 |   | eleq1 2259 | 
. . . . . 6
⊢ (𝑥 = suc 𝑦 → (𝑥 ∈ 𝑥 ↔ suc 𝑦 ∈ 𝑥)) | 
| 34 |   | eleq2 2260 | 
. . . . . 6
⊢ (𝑥 = suc 𝑦 → (suc 𝑦 ∈ 𝑥 ↔ suc 𝑦 ∈ suc 𝑦)) | 
| 35 | 33, 34 | bitrd 188 | 
. . . . 5
⊢ (𝑥 = suc 𝑦 → (𝑥 ∈ 𝑥 ↔ suc 𝑦 ∈ suc 𝑦)) | 
| 36 | 35 | notbid 668 | 
. . . 4
⊢ (𝑥 = suc 𝑦 → (¬ 𝑥 ∈ 𝑥 ↔ ¬ suc 𝑦 ∈ suc 𝑦)) | 
| 37 | 36 | biimprd 158 | 
. . 3
⊢ (𝑥 = suc 𝑦 → (¬ suc 𝑦 ∈ suc 𝑦 → ¬ 𝑥 ∈ 𝑥)) | 
| 38 |   | nfcv 2339 | 
. . 3
⊢
Ⅎ𝑥𝐴 | 
| 39 |   | nfv 1542 | 
. . 3
⊢
Ⅎ𝑥 ¬ 𝐴 ∈ 𝐴 | 
| 40 |   | eleq1 2259 | 
. . . . . 6
⊢ (𝑥 = 𝐴 → (𝑥 ∈ 𝑥 ↔ 𝐴 ∈ 𝑥)) | 
| 41 |   | eleq2 2260 | 
. . . . . 6
⊢ (𝑥 = 𝐴 → (𝐴 ∈ 𝑥 ↔ 𝐴 ∈ 𝐴)) | 
| 42 | 40, 41 | bitrd 188 | 
. . . . 5
⊢ (𝑥 = 𝐴 → (𝑥 ∈ 𝑥 ↔ 𝐴 ∈ 𝐴)) | 
| 43 | 42 | notbid 668 | 
. . . 4
⊢ (𝑥 = 𝐴 → (¬ 𝑥 ∈ 𝑥 ↔ ¬ 𝐴 ∈ 𝐴)) | 
| 44 | 43 | biimpd 144 | 
. . 3
⊢ (𝑥 = 𝐴 → (¬ 𝑥 ∈ 𝑥 → ¬ 𝐴 ∈ 𝐴)) | 
| 45 | 19, 20, 21, 22, 27, 32, 37, 38, 39, 44 | bj-bdfindisg 15594 | 
. 2
⊢ ((¬
∅ ∈ ∅ ∧ ∀𝑦 ∈ ω (¬ 𝑦 ∈ 𝑦 → ¬ suc 𝑦 ∈ suc 𝑦)) → (𝐴 ∈ ω → ¬ 𝐴 ∈ 𝐴)) | 
| 46 | 1, 17, 45 | mp2an 426 | 
1
⊢ (𝐴 ∈ ω → ¬
𝐴 ∈ 𝐴) |