| Step | Hyp | Ref
 | Expression | 
| 1 |   | vex 2766 | 
. . . 4
⊢ 𝑥 ∈ V | 
| 2 |   | id 19 | 
. . . . . . 7
⊢ (𝑥 = 𝑧 → 𝑥 = 𝑧) | 
| 3 |   | csbeq1a 3093 | 
. . . . . . 7
⊢ (𝑥 = 𝑧 → 𝐴 = ⦋𝑧 / 𝑥⦌𝐴) | 
| 4 | 2, 3 | eleq12d 2267 | 
. . . . . 6
⊢ (𝑥 = 𝑧 → (𝑥 ∈ 𝐴 ↔ 𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴)) | 
| 5 |   | csbeq1a 3093 | 
. . . . . . 7
⊢ (𝑥 = 𝑧 → 𝐵 = ⦋𝑧 / 𝑥⦌𝐵) | 
| 6 | 5 | biantrud 304 | 
. . . . . 6
⊢ (𝑥 = 𝑧 → (𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ↔ (𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝐵 = ⦋𝑧 / 𝑥⦌𝐵))) | 
| 7 | 4, 6 | bitr2d 189 | 
. . . . 5
⊢ (𝑥 = 𝑧 → ((𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝐵 = ⦋𝑧 / 𝑥⦌𝐵) ↔ 𝑥 ∈ 𝐴)) | 
| 8 | 7 | equcoms 1722 | 
. . . 4
⊢ (𝑧 = 𝑥 → ((𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝐵 = ⦋𝑧 / 𝑥⦌𝐵) ↔ 𝑥 ∈ 𝐴)) | 
| 9 | 1, 8 | spcev 2859 | 
. . 3
⊢ (𝑥 ∈ 𝐴 → ∃𝑧(𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝐵 = ⦋𝑧 / 𝑥⦌𝐵)) | 
| 10 |   | df-rex 2481 | 
. . . . . 6
⊢
(∃𝑥 ∈
𝐴 𝑦 = 𝐵 ↔ ∃𝑥(𝑥 ∈ 𝐴 ∧ 𝑦 = 𝐵)) | 
| 11 |   | nfv 1542 | 
. . . . . . 7
⊢
Ⅎ𝑧(𝑥 ∈ 𝐴 ∧ 𝑦 = 𝐵) | 
| 12 |   | nfcsb1v 3117 | 
. . . . . . . . 9
⊢
Ⅎ𝑥⦋𝑧 / 𝑥⦌𝐴 | 
| 13 | 12 | nfcri 2333 | 
. . . . . . . 8
⊢
Ⅎ𝑥 𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 | 
| 14 |   | nfcsb1v 3117 | 
. . . . . . . . 9
⊢
Ⅎ𝑥⦋𝑧 / 𝑥⦌𝐵 | 
| 15 | 14 | nfeq2 2351 | 
. . . . . . . 8
⊢
Ⅎ𝑥 𝑦 = ⦋𝑧 / 𝑥⦌𝐵 | 
| 16 | 13, 15 | nfan 1579 | 
. . . . . . 7
⊢
Ⅎ𝑥(𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝑦 = ⦋𝑧 / 𝑥⦌𝐵) | 
| 17 | 5 | eqeq2d 2208 | 
. . . . . . . 8
⊢ (𝑥 = 𝑧 → (𝑦 = 𝐵 ↔ 𝑦 = ⦋𝑧 / 𝑥⦌𝐵)) | 
| 18 | 4, 17 | anbi12d 473 | 
. . . . . . 7
⊢ (𝑥 = 𝑧 → ((𝑥 ∈ 𝐴 ∧ 𝑦 = 𝐵) ↔ (𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝑦 = ⦋𝑧 / 𝑥⦌𝐵))) | 
| 19 | 11, 16, 18 | cbvex 1770 | 
. . . . . 6
⊢
(∃𝑥(𝑥 ∈ 𝐴 ∧ 𝑦 = 𝐵) ↔ ∃𝑧(𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝑦 = ⦋𝑧 / 𝑥⦌𝐵)) | 
| 20 | 10, 19 | bitri 184 | 
. . . . 5
⊢
(∃𝑥 ∈
𝐴 𝑦 = 𝐵 ↔ ∃𝑧(𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝑦 = ⦋𝑧 / 𝑥⦌𝐵)) | 
| 21 |   | eqeq1 2203 | 
. . . . . . 7
⊢ (𝑦 = 𝐵 → (𝑦 = ⦋𝑧 / 𝑥⦌𝐵 ↔ 𝐵 = ⦋𝑧 / 𝑥⦌𝐵)) | 
| 22 | 21 | anbi2d 464 | 
. . . . . 6
⊢ (𝑦 = 𝐵 → ((𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝑦 = ⦋𝑧 / 𝑥⦌𝐵) ↔ (𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝐵 = ⦋𝑧 / 𝑥⦌𝐵))) | 
| 23 | 22 | exbidv 1839 | 
. . . . 5
⊢ (𝑦 = 𝐵 → (∃𝑧(𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝑦 = ⦋𝑧 / 𝑥⦌𝐵) ↔ ∃𝑧(𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝐵 = ⦋𝑧 / 𝑥⦌𝐵))) | 
| 24 | 20, 23 | bitrid 192 | 
. . . 4
⊢ (𝑦 = 𝐵 → (∃𝑥 ∈ 𝐴 𝑦 = 𝐵 ↔ ∃𝑧(𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝐵 = ⦋𝑧 / 𝑥⦌𝐵))) | 
| 25 |   | rnmpt.1 | 
. . . . 5
⊢ 𝐹 = (𝑥 ∈ 𝐴 ↦ 𝐵) | 
| 26 | 25 | rnmpt 4914 | 
. . . 4
⊢ ran 𝐹 = {𝑦 ∣ ∃𝑥 ∈ 𝐴 𝑦 = 𝐵} | 
| 27 | 24, 26 | elab2g 2911 | 
. . 3
⊢ (𝐵 ∈ 𝑉 → (𝐵 ∈ ran 𝐹 ↔ ∃𝑧(𝑧 ∈ ⦋𝑧 / 𝑥⦌𝐴 ∧ 𝐵 = ⦋𝑧 / 𝑥⦌𝐵))) | 
| 28 | 9, 27 | imbitrrid 156 | 
. 2
⊢ (𝐵 ∈ 𝑉 → (𝑥 ∈ 𝐴 → 𝐵 ∈ ran 𝐹)) | 
| 29 | 28 | impcom 125 | 
1
⊢ ((𝑥 ∈ 𝐴 ∧ 𝐵 ∈ 𝑉) → 𝐵 ∈ ran 𝐹) |