| Step | Hyp | Ref
 | Expression | 
| 1 |   | nfv 1542 | 
. . . 4
⊢
Ⅎ𝑧(𝑥 ∈ 𝐴 ∧ 𝜑) | 
| 2 |   | nfcsb1v 3117 | 
. . . . . 6
⊢
Ⅎ𝑥⦋𝑧 / 𝑥⦌𝐴 | 
| 3 | 2 | nfcri 2333 | 
. . . . 5
⊢
Ⅎ𝑥 𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 | 
| 4 |   | nfs1v 1958 | 
. . . . 5
⊢
Ⅎ𝑥[𝑧 / 𝑥]𝜑 | 
| 5 | 3, 4 | nfan 1579 | 
. . . 4
⊢
Ⅎ𝑥(𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ [𝑧 / 𝑥]𝜑) | 
| 6 |   | id 19 | 
. . . . . 6
⊢ (𝑥 = 𝑧 → 𝑥 = 𝑧) | 
| 7 |   | csbeq1a 3093 | 
. . . . . 6
⊢ (𝑥 = 𝑧 → 𝐴 = ⦋𝑧 / 𝑥⦌𝐴) | 
| 8 | 6, 7 | eleq12d 2267 | 
. . . . 5
⊢ (𝑥 = 𝑧 → (𝑥 ∈ 𝐴 ↔ 𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴)) | 
| 9 |   | sbequ12 1785 | 
. . . . 5
⊢ (𝑥 = 𝑧 → (𝜑 ↔ [𝑧 / 𝑥]𝜑)) | 
| 10 | 8, 9 | anbi12d 473 | 
. . . 4
⊢ (𝑥 = 𝑧 → ((𝑥 ∈ 𝐴 ∧ 𝜑) ↔ (𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ [𝑧 / 𝑥]𝜑))) | 
| 11 | 1, 5, 10 | cbveu 2069 | 
. . 3
⊢
(∃!𝑥(𝑥 ∈ 𝐴 ∧ 𝜑) ↔ ∃!𝑧(𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ [𝑧 / 𝑥]𝜑)) | 
| 12 |   | nfcv 2339 | 
. . . . . . 7
⊢
Ⅎ𝑦𝑧 | 
| 13 |   | cbvralcsf.1 | 
. . . . . . 7
⊢
Ⅎ𝑦𝐴 | 
| 14 | 12, 13 | nfcsb 3122 | 
. . . . . 6
⊢
Ⅎ𝑦⦋𝑧 / 𝑥⦌𝐴 | 
| 15 | 14 | nfcri 2333 | 
. . . . 5
⊢
Ⅎ𝑦 𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 | 
| 16 |   | cbvralcsf.3 | 
. . . . . 6
⊢
Ⅎ𝑦𝜑 | 
| 17 | 16 | nfsb 1965 | 
. . . . 5
⊢
Ⅎ𝑦[𝑧 / 𝑥]𝜑 | 
| 18 | 15, 17 | nfan 1579 | 
. . . 4
⊢
Ⅎ𝑦(𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ [𝑧 / 𝑥]𝜑) | 
| 19 |   | nfv 1542 | 
. . . 4
⊢
Ⅎ𝑧(𝑦 ∈ 𝐵 ∧ 𝜓) | 
| 20 |   | id 19 | 
. . . . . 6
⊢ (𝑧 = 𝑦 → 𝑧 = 𝑦) | 
| 21 |   | csbeq1 3087 | 
. . . . . . 7
⊢ (𝑧 = 𝑦 → ⦋𝑧 / 𝑥⦌𝐴 = ⦋𝑦 / 𝑥⦌𝐴) | 
| 22 |   | sbsbc 2993 | 
. . . . . . . . 9
⊢ ([𝑦 / 𝑥]𝑣 ∈ 𝐴 ↔ [𝑦 / 𝑥]𝑣 ∈ 𝐴) | 
| 23 | 22 | abbii 2312 | 
. . . . . . . 8
⊢ {𝑣 ∣ [𝑦 / 𝑥]𝑣 ∈ 𝐴} = {𝑣 ∣ [𝑦 / 𝑥]𝑣 ∈ 𝐴} | 
| 24 |   | cbvralcsf.2 | 
. . . . . . . . . . . 12
⊢
Ⅎ𝑥𝐵 | 
| 25 | 24 | nfcri 2333 | 
. . . . . . . . . . 11
⊢
Ⅎ𝑥 𝑣 ∈ 𝐵 | 
| 26 |   | cbvralcsf.5 | 
. . . . . . . . . . . 12
⊢ (𝑥 = 𝑦 → 𝐴 = 𝐵) | 
| 27 | 26 | eleq2d 2266 | 
. . . . . . . . . . 11
⊢ (𝑥 = 𝑦 → (𝑣 ∈ 𝐴 ↔ 𝑣 ∈ 𝐵)) | 
| 28 | 25, 27 | sbie 1805 | 
. . . . . . . . . 10
⊢ ([𝑦 / 𝑥]𝑣 ∈ 𝐴 ↔ 𝑣 ∈ 𝐵) | 
| 29 | 28 | bicomi 132 | 
. . . . . . . . 9
⊢ (𝑣 ∈ 𝐵 ↔ [𝑦 / 𝑥]𝑣 ∈ 𝐴) | 
| 30 | 29 | abbi2i 2311 | 
. . . . . . . 8
⊢ 𝐵 = {𝑣 ∣ [𝑦 / 𝑥]𝑣 ∈ 𝐴} | 
| 31 |   | df-csb 3085 | 
. . . . . . . 8
⊢
⦋𝑦 /
𝑥⦌𝐴 = {𝑣 ∣ [𝑦 / 𝑥]𝑣 ∈ 𝐴} | 
| 32 | 23, 30, 31 | 3eqtr4ri 2228 | 
. . . . . . 7
⊢
⦋𝑦 /
𝑥⦌𝐴 = 𝐵 | 
| 33 | 21, 32 | eqtrdi 2245 | 
. . . . . 6
⊢ (𝑧 = 𝑦 → ⦋𝑧 / 𝑥⦌𝐴 = 𝐵) | 
| 34 | 20, 33 | eleq12d 2267 | 
. . . . 5
⊢ (𝑧 = 𝑦 → (𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ↔ 𝑦 ∈ 𝐵)) | 
| 35 |   | sbequ 1854 | 
. . . . . 6
⊢ (𝑧 = 𝑦 → ([𝑧 / 𝑥]𝜑 ↔ [𝑦 / 𝑥]𝜑)) | 
| 36 |   | cbvralcsf.4 | 
. . . . . . 7
⊢
Ⅎ𝑥𝜓 | 
| 37 |   | cbvralcsf.6 | 
. . . . . . 7
⊢ (𝑥 = 𝑦 → (𝜑 ↔ 𝜓)) | 
| 38 | 36, 37 | sbie 1805 | 
. . . . . 6
⊢ ([𝑦 / 𝑥]𝜑 ↔ 𝜓) | 
| 39 | 35, 38 | bitrdi 196 | 
. . . . 5
⊢ (𝑧 = 𝑦 → ([𝑧 / 𝑥]𝜑 ↔ 𝜓)) | 
| 40 | 34, 39 | anbi12d 473 | 
. . . 4
⊢ (𝑧 = 𝑦 → ((𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ [𝑧 / 𝑥]𝜑) ↔ (𝑦 ∈ 𝐵 ∧ 𝜓))) | 
| 41 | 18, 19, 40 | cbveu 2069 | 
. . 3
⊢
(∃!𝑧(𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ [𝑧 / 𝑥]𝜑) ↔ ∃!𝑦(𝑦 ∈ 𝐵 ∧ 𝜓)) | 
| 42 | 11, 41 | bitri 184 | 
. 2
⊢
(∃!𝑥(𝑥 ∈ 𝐴 ∧ 𝜑) ↔ ∃!𝑦(𝑦 ∈ 𝐵 ∧ 𝜓)) | 
| 43 |   | df-reu 2482 | 
. 2
⊢
(∃!𝑥 ∈
𝐴 𝜑 ↔ ∃!𝑥(𝑥 ∈ 𝐴 ∧ 𝜑)) | 
| 44 |   | df-reu 2482 | 
. 2
⊢
(∃!𝑦 ∈
𝐵 𝜓 ↔ ∃!𝑦(𝑦 ∈ 𝐵 ∧ 𝜓)) | 
| 45 | 42, 43, 44 | 3bitr4i 212 | 
1
⊢
(∃!𝑥 ∈
𝐴 𝜑 ↔ ∃!𝑦 ∈ 𝐵 𝜓) |