| Step | Hyp | Ref
 | Expression | 
| 1 |   | vex 2766 | 
. . . . . 6
⊢ 𝑢 ∈ V | 
| 2 |   | vex 2766 | 
. . . . . 6
⊢ 𝑣 ∈ V | 
| 3 | 1, 2 | op1std 6206 | 
. . . . 5
⊢ (𝑧 = 〈𝑢, 𝑣〉 → (1st ‘𝑧) = 𝑢) | 
| 4 | 3 | csbeq1d 3091 | 
. . . 4
⊢ (𝑧 = 〈𝑢, 𝑣〉 → ⦋(1st
‘𝑧) / 𝑥⦌⦋(2nd
‘𝑧) / 𝑦⦌𝐶 = ⦋𝑢 / 𝑥⦌⦋(2nd
‘𝑧) / 𝑦⦌𝐶) | 
| 5 | 1, 2 | op2ndd 6207 | 
. . . . . 6
⊢ (𝑧 = 〈𝑢, 𝑣〉 → (2nd ‘𝑧) = 𝑣) | 
| 6 | 5 | csbeq1d 3091 | 
. . . . 5
⊢ (𝑧 = 〈𝑢, 𝑣〉 → ⦋(2nd
‘𝑧) / 𝑦⦌𝐶 = ⦋𝑣 / 𝑦⦌𝐶) | 
| 7 | 6 | csbeq2dv 3110 | 
. . . 4
⊢ (𝑧 = 〈𝑢, 𝑣〉 → ⦋𝑢 / 𝑥⦌⦋(2nd
‘𝑧) / 𝑦⦌𝐶 = ⦋𝑢 / 𝑥⦌⦋𝑣 / 𝑦⦌𝐶) | 
| 8 | 4, 7 | eqtrd 2229 | 
. . 3
⊢ (𝑧 = 〈𝑢, 𝑣〉 → ⦋(1st
‘𝑧) / 𝑥⦌⦋(2nd
‘𝑧) / 𝑦⦌𝐶 = ⦋𝑢 / 𝑥⦌⦋𝑣 / 𝑦⦌𝐶) | 
| 9 | 8 | mpomptx 6013 | 
. 2
⊢ (𝑧 ∈ ∪ 𝑢 ∈ 𝐴 ({𝑢} × ⦋𝑢 / 𝑥⦌𝐵) ↦ ⦋(1st
‘𝑧) / 𝑥⦌⦋(2nd
‘𝑧) / 𝑦⦌𝐶) = (𝑢 ∈ 𝐴, 𝑣 ∈ ⦋𝑢 / 𝑥⦌𝐵 ↦ ⦋𝑢 / 𝑥⦌⦋𝑣 / 𝑦⦌𝐶) | 
| 10 |   | nfcv 2339 | 
. . . 4
⊢
Ⅎ𝑢({𝑥} × 𝐵) | 
| 11 |   | nfcv 2339 | 
. . . . 5
⊢
Ⅎ𝑥{𝑢} | 
| 12 |   | nfcsb1v 3117 | 
. . . . 5
⊢
Ⅎ𝑥⦋𝑢 / 𝑥⦌𝐵 | 
| 13 | 11, 12 | nfxp 4690 | 
. . . 4
⊢
Ⅎ𝑥({𝑢} × ⦋𝑢 / 𝑥⦌𝐵) | 
| 14 |   | sneq 3633 | 
. . . . 5
⊢ (𝑥 = 𝑢 → {𝑥} = {𝑢}) | 
| 15 |   | csbeq1a 3093 | 
. . . . 5
⊢ (𝑥 = 𝑢 → 𝐵 = ⦋𝑢 / 𝑥⦌𝐵) | 
| 16 | 14, 15 | xpeq12d 4688 | 
. . . 4
⊢ (𝑥 = 𝑢 → ({𝑥} × 𝐵) = ({𝑢} × ⦋𝑢 / 𝑥⦌𝐵)) | 
| 17 | 10, 13, 16 | cbviun 3953 | 
. . 3
⊢ ∪ 𝑥 ∈ 𝐴 ({𝑥} × 𝐵) = ∪
𝑢 ∈ 𝐴 ({𝑢} × ⦋𝑢 / 𝑥⦌𝐵) | 
| 18 |   | mpteq1 4117 | 
. . 3
⊢ (∪ 𝑥 ∈ 𝐴 ({𝑥} × 𝐵) = ∪
𝑢 ∈ 𝐴 ({𝑢} × ⦋𝑢 / 𝑥⦌𝐵) → (𝑧 ∈ ∪
𝑥 ∈ 𝐴 ({𝑥} × 𝐵) ↦ ⦋(1st
‘𝑧) / 𝑥⦌⦋(2nd
‘𝑧) / 𝑦⦌𝐶) = (𝑧 ∈ ∪
𝑢 ∈ 𝐴 ({𝑢} × ⦋𝑢 / 𝑥⦌𝐵) ↦ ⦋(1st
‘𝑧) / 𝑥⦌⦋(2nd
‘𝑧) / 𝑦⦌𝐶)) | 
| 19 | 17, 18 | ax-mp 5 | 
. 2
⊢ (𝑧 ∈ ∪ 𝑥 ∈ 𝐴 ({𝑥} × 𝐵) ↦ ⦋(1st
‘𝑧) / 𝑥⦌⦋(2nd
‘𝑧) / 𝑦⦌𝐶) = (𝑧 ∈ ∪
𝑢 ∈ 𝐴 ({𝑢} × ⦋𝑢 / 𝑥⦌𝐵) ↦ ⦋(1st
‘𝑧) / 𝑥⦌⦋(2nd
‘𝑧) / 𝑦⦌𝐶) | 
| 20 |   | nfcv 2339 | 
. . 3
⊢
Ⅎ𝑢𝐵 | 
| 21 |   | nfcv 2339 | 
. . 3
⊢
Ⅎ𝑢𝐶 | 
| 22 |   | nfcv 2339 | 
. . 3
⊢
Ⅎ𝑣𝐶 | 
| 23 |   | nfcsb1v 3117 | 
. . 3
⊢
Ⅎ𝑥⦋𝑢 / 𝑥⦌⦋𝑣 / 𝑦⦌𝐶 | 
| 24 |   | nfcv 2339 | 
. . . 4
⊢
Ⅎ𝑦𝑢 | 
| 25 |   | nfcsb1v 3117 | 
. . . 4
⊢
Ⅎ𝑦⦋𝑣 / 𝑦⦌𝐶 | 
| 26 | 24, 25 | nfcsb 3122 | 
. . 3
⊢
Ⅎ𝑦⦋𝑢 / 𝑥⦌⦋𝑣 / 𝑦⦌𝐶 | 
| 27 |   | csbeq1a 3093 | 
. . . 4
⊢ (𝑦 = 𝑣 → 𝐶 = ⦋𝑣 / 𝑦⦌𝐶) | 
| 28 |   | csbeq1a 3093 | 
. . . 4
⊢ (𝑥 = 𝑢 → ⦋𝑣 / 𝑦⦌𝐶 = ⦋𝑢 / 𝑥⦌⦋𝑣 / 𝑦⦌𝐶) | 
| 29 | 27, 28 | sylan9eqr 2251 | 
. . 3
⊢ ((𝑥 = 𝑢 ∧ 𝑦 = 𝑣) → 𝐶 = ⦋𝑢 / 𝑥⦌⦋𝑣 / 𝑦⦌𝐶) | 
| 30 | 20, 12, 21, 22, 23, 26, 15, 29 | cbvmpox 6000 | 
. 2
⊢ (𝑥 ∈ 𝐴, 𝑦 ∈ 𝐵 ↦ 𝐶) = (𝑢 ∈ 𝐴, 𝑣 ∈ ⦋𝑢 / 𝑥⦌𝐵 ↦ ⦋𝑢 / 𝑥⦌⦋𝑣 / 𝑦⦌𝐶) | 
| 31 | 9, 19, 30 | 3eqtr4ri 2228 | 
1
⊢ (𝑥 ∈ 𝐴, 𝑦 ∈ 𝐵 ↦ 𝐶) = (𝑧 ∈ ∪
𝑥 ∈ 𝐴 ({𝑥} × 𝐵) ↦ ⦋(1st
‘𝑧) / 𝑥⦌⦋(2nd
‘𝑧) / 𝑦⦌𝐶) |