| Step | Hyp | Ref
 | Expression | 
| 1 |   | bdcriota.bd | 
. . . . . . . . 9
⊢
BOUNDED 𝜑 | 
| 2 | 1 | ax-bdsb 15468 | 
. . . . . . . 8
⊢
BOUNDED [𝑧 / 𝑥]𝜑 | 
| 3 |   | ax-bdel 15467 | 
. . . . . . . 8
⊢
BOUNDED 𝑡 ∈ 𝑧 | 
| 4 | 2, 3 | ax-bdim 15460 | 
. . . . . . 7
⊢
BOUNDED ([𝑧 / 𝑥]𝜑 → 𝑡 ∈ 𝑧) | 
| 5 | 4 | ax-bdal 15464 | 
. . . . . 6
⊢
BOUNDED ∀𝑧 ∈ 𝑦 ([𝑧 / 𝑥]𝜑 → 𝑡 ∈ 𝑧) | 
| 6 |   | df-ral 2480 | 
. . . . . . . . 9
⊢
(∀𝑧 ∈
𝑦 ([𝑧 / 𝑥]𝜑 → 𝑡 ∈ 𝑧) ↔ ∀𝑧(𝑧 ∈ 𝑦 → ([𝑧 / 𝑥]𝜑 → 𝑡 ∈ 𝑧))) | 
| 7 |   | impexp 263 | 
. . . . . . . . . . 11
⊢ (((𝑧 ∈ 𝑦 ∧ [𝑧 / 𝑥]𝜑) → 𝑡 ∈ 𝑧) ↔ (𝑧 ∈ 𝑦 → ([𝑧 / 𝑥]𝜑 → 𝑡 ∈ 𝑧))) | 
| 8 | 7 | bicomi 132 | 
. . . . . . . . . 10
⊢ ((𝑧 ∈ 𝑦 → ([𝑧 / 𝑥]𝜑 → 𝑡 ∈ 𝑧)) ↔ ((𝑧 ∈ 𝑦 ∧ [𝑧 / 𝑥]𝜑) → 𝑡 ∈ 𝑧)) | 
| 9 | 8 | albii 1484 | 
. . . . . . . . 9
⊢
(∀𝑧(𝑧 ∈ 𝑦 → ([𝑧 / 𝑥]𝜑 → 𝑡 ∈ 𝑧)) ↔ ∀𝑧((𝑧 ∈ 𝑦 ∧ [𝑧 / 𝑥]𝜑) → 𝑡 ∈ 𝑧)) | 
| 10 | 6, 9 | bitri 184 | 
. . . . . . . 8
⊢
(∀𝑧 ∈
𝑦 ([𝑧 / 𝑥]𝜑 → 𝑡 ∈ 𝑧) ↔ ∀𝑧((𝑧 ∈ 𝑦 ∧ [𝑧 / 𝑥]𝜑) → 𝑡 ∈ 𝑧)) | 
| 11 |   | sban 1974 | 
. . . . . . . . . . . 12
⊢ ([𝑧 / 𝑥](𝑥 ∈ 𝑦 ∧ 𝜑) ↔ ([𝑧 / 𝑥]𝑥 ∈ 𝑦 ∧ [𝑧 / 𝑥]𝜑)) | 
| 12 |   | clelsb1 2301 | 
. . . . . . . . . . . . 13
⊢ ([𝑧 / 𝑥]𝑥 ∈ 𝑦 ↔ 𝑧 ∈ 𝑦) | 
| 13 | 12 | anbi1i 458 | 
. . . . . . . . . . . 12
⊢ (([𝑧 / 𝑥]𝑥 ∈ 𝑦 ∧ [𝑧 / 𝑥]𝜑) ↔ (𝑧 ∈ 𝑦 ∧ [𝑧 / 𝑥]𝜑)) | 
| 14 | 11, 13 | bitri 184 | 
. . . . . . . . . . 11
⊢ ([𝑧 / 𝑥](𝑥 ∈ 𝑦 ∧ 𝜑) ↔ (𝑧 ∈ 𝑦 ∧ [𝑧 / 𝑥]𝜑)) | 
| 15 | 14 | bicomi 132 | 
. . . . . . . . . 10
⊢ ((𝑧 ∈ 𝑦 ∧ [𝑧 / 𝑥]𝜑) ↔ [𝑧 / 𝑥](𝑥 ∈ 𝑦 ∧ 𝜑)) | 
| 16 | 15 | imbi1i 238 | 
. . . . . . . . 9
⊢ (((𝑧 ∈ 𝑦 ∧ [𝑧 / 𝑥]𝜑) → 𝑡 ∈ 𝑧) ↔ ([𝑧 / 𝑥](𝑥 ∈ 𝑦 ∧ 𝜑) → 𝑡 ∈ 𝑧)) | 
| 17 | 16 | albii 1484 | 
. . . . . . . 8
⊢
(∀𝑧((𝑧 ∈ 𝑦 ∧ [𝑧 / 𝑥]𝜑) → 𝑡 ∈ 𝑧) ↔ ∀𝑧([𝑧 / 𝑥](𝑥 ∈ 𝑦 ∧ 𝜑) → 𝑡 ∈ 𝑧)) | 
| 18 | 10, 17 | bitri 184 | 
. . . . . . 7
⊢
(∀𝑧 ∈
𝑦 ([𝑧 / 𝑥]𝜑 → 𝑡 ∈ 𝑧) ↔ ∀𝑧([𝑧 / 𝑥](𝑥 ∈ 𝑦 ∧ 𝜑) → 𝑡 ∈ 𝑧)) | 
| 19 |   | df-clab 2183 | 
. . . . . . . . . 10
⊢ (𝑧 ∈ {𝑥 ∣ (𝑥 ∈ 𝑦 ∧ 𝜑)} ↔ [𝑧 / 𝑥](𝑥 ∈ 𝑦 ∧ 𝜑)) | 
| 20 | 19 | bicomi 132 | 
. . . . . . . . 9
⊢ ([𝑧 / 𝑥](𝑥 ∈ 𝑦 ∧ 𝜑) ↔ 𝑧 ∈ {𝑥 ∣ (𝑥 ∈ 𝑦 ∧ 𝜑)}) | 
| 21 | 20 | imbi1i 238 | 
. . . . . . . 8
⊢ (([𝑧 / 𝑥](𝑥 ∈ 𝑦 ∧ 𝜑) → 𝑡 ∈ 𝑧) ↔ (𝑧 ∈ {𝑥 ∣ (𝑥 ∈ 𝑦 ∧ 𝜑)} → 𝑡 ∈ 𝑧)) | 
| 22 | 21 | albii 1484 | 
. . . . . . 7
⊢
(∀𝑧([𝑧 / 𝑥](𝑥 ∈ 𝑦 ∧ 𝜑) → 𝑡 ∈ 𝑧) ↔ ∀𝑧(𝑧 ∈ {𝑥 ∣ (𝑥 ∈ 𝑦 ∧ 𝜑)} → 𝑡 ∈ 𝑧)) | 
| 23 | 18, 22 | bitri 184 | 
. . . . . 6
⊢
(∀𝑧 ∈
𝑦 ([𝑧 / 𝑥]𝜑 → 𝑡 ∈ 𝑧) ↔ ∀𝑧(𝑧 ∈ {𝑥 ∣ (𝑥 ∈ 𝑦 ∧ 𝜑)} → 𝑡 ∈ 𝑧)) | 
| 24 | 5, 23 | bd0 15470 | 
. . . . 5
⊢
BOUNDED ∀𝑧(𝑧 ∈ {𝑥 ∣ (𝑥 ∈ 𝑦 ∧ 𝜑)} → 𝑡 ∈ 𝑧) | 
| 25 | 24 | bdcab 15495 | 
. . . 4
⊢
BOUNDED {𝑡 ∣ ∀𝑧(𝑧 ∈ {𝑥 ∣ (𝑥 ∈ 𝑦 ∧ 𝜑)} → 𝑡 ∈ 𝑧)} | 
| 26 |   | df-int 3875 | 
. . . 4
⊢ ∩ {𝑥
∣ (𝑥 ∈ 𝑦 ∧ 𝜑)} = {𝑡 ∣ ∀𝑧(𝑧 ∈ {𝑥 ∣ (𝑥 ∈ 𝑦 ∧ 𝜑)} → 𝑡 ∈ 𝑧)} | 
| 27 | 25, 26 | bdceqir 15490 | 
. . 3
⊢
BOUNDED ∩ {𝑥 ∣ (𝑥 ∈ 𝑦 ∧ 𝜑)} | 
| 28 |   | bdcriota.ex | 
. . . . 5
⊢
∃!𝑥 ∈
𝑦 𝜑 | 
| 29 |   | df-reu 2482 | 
. . . . 5
⊢
(∃!𝑥 ∈
𝑦 𝜑 ↔ ∃!𝑥(𝑥 ∈ 𝑦 ∧ 𝜑)) | 
| 30 | 28, 29 | mpbi 145 | 
. . . 4
⊢
∃!𝑥(𝑥 ∈ 𝑦 ∧ 𝜑) | 
| 31 |   | iotaint 5232 | 
. . . 4
⊢
(∃!𝑥(𝑥 ∈ 𝑦 ∧ 𝜑) → (℩𝑥(𝑥 ∈ 𝑦 ∧ 𝜑)) = ∩ {𝑥 ∣ (𝑥 ∈ 𝑦 ∧ 𝜑)}) | 
| 32 | 30, 31 | ax-mp 5 | 
. . 3
⊢
(℩𝑥(𝑥 ∈ 𝑦 ∧ 𝜑)) = ∩ {𝑥 ∣ (𝑥 ∈ 𝑦 ∧ 𝜑)} | 
| 33 | 27, 32 | bdceqir 15490 | 
. 2
⊢
BOUNDED (℩𝑥(𝑥 ∈ 𝑦 ∧ 𝜑)) | 
| 34 |   | df-riota 5877 | 
. 2
⊢
(℩𝑥
∈ 𝑦 𝜑) = (℩𝑥(𝑥 ∈ 𝑦 ∧ 𝜑)) | 
| 35 | 33, 34 | bdceqir 15490 | 
1
⊢
BOUNDED (℩𝑥 ∈ 𝑦 𝜑) |