| Step | Hyp | Ref
 | Expression | 
| 1 |   | nfa1 1555 | 
. . . 4
⊢
Ⅎ𝑥∀𝑥 𝐴 = 𝐶 | 
| 2 |   | nfra1 2528 | 
. . . 4
⊢
Ⅎ𝑥∀𝑥 ∈ 𝐴 𝐵 = 𝐷 | 
| 3 | 1, 2 | nfan 1579 | 
. . 3
⊢
Ⅎ𝑥(∀𝑥 𝐴 = 𝐶 ∧ ∀𝑥 ∈ 𝐴 𝐵 = 𝐷) | 
| 4 |   | nfv 1542 | 
. . 3
⊢
Ⅎ𝑦(∀𝑥 𝐴 = 𝐶 ∧ ∀𝑥 ∈ 𝐴 𝐵 = 𝐷) | 
| 5 |   | rsp 2544 | 
. . . . . . 7
⊢
(∀𝑥 ∈
𝐴 𝐵 = 𝐷 → (𝑥 ∈ 𝐴 → 𝐵 = 𝐷)) | 
| 6 | 5 | imp 124 | 
. . . . . 6
⊢
((∀𝑥 ∈
𝐴 𝐵 = 𝐷 ∧ 𝑥 ∈ 𝐴) → 𝐵 = 𝐷) | 
| 7 | 6 | eqeq2d 2208 | 
. . . . 5
⊢
((∀𝑥 ∈
𝐴 𝐵 = 𝐷 ∧ 𝑥 ∈ 𝐴) → (𝑦 = 𝐵 ↔ 𝑦 = 𝐷)) | 
| 8 | 7 | pm5.32da 452 | 
. . . 4
⊢
(∀𝑥 ∈
𝐴 𝐵 = 𝐷 → ((𝑥 ∈ 𝐴 ∧ 𝑦 = 𝐵) ↔ (𝑥 ∈ 𝐴 ∧ 𝑦 = 𝐷))) | 
| 9 |   | sp 1525 | 
. . . . . 6
⊢
(∀𝑥 𝐴 = 𝐶 → 𝐴 = 𝐶) | 
| 10 | 9 | eleq2d 2266 | 
. . . . 5
⊢
(∀𝑥 𝐴 = 𝐶 → (𝑥 ∈ 𝐴 ↔ 𝑥 ∈ 𝐶)) | 
| 11 | 10 | anbi1d 465 | 
. . . 4
⊢
(∀𝑥 𝐴 = 𝐶 → ((𝑥 ∈ 𝐴 ∧ 𝑦 = 𝐷) ↔ (𝑥 ∈ 𝐶 ∧ 𝑦 = 𝐷))) | 
| 12 | 8, 11 | sylan9bbr 463 | 
. . 3
⊢
((∀𝑥 𝐴 = 𝐶 ∧ ∀𝑥 ∈ 𝐴 𝐵 = 𝐷) → ((𝑥 ∈ 𝐴 ∧ 𝑦 = 𝐵) ↔ (𝑥 ∈ 𝐶 ∧ 𝑦 = 𝐷))) | 
| 13 | 3, 4, 12 | opabbid 4098 | 
. 2
⊢
((∀𝑥 𝐴 = 𝐶 ∧ ∀𝑥 ∈ 𝐴 𝐵 = 𝐷) → {〈𝑥, 𝑦〉 ∣ (𝑥 ∈ 𝐴 ∧ 𝑦 = 𝐵)} = {〈𝑥, 𝑦〉 ∣ (𝑥 ∈ 𝐶 ∧ 𝑦 = 𝐷)}) | 
| 14 |   | df-mpt 4096 | 
. 2
⊢ (𝑥 ∈ 𝐴 ↦ 𝐵) = {〈𝑥, 𝑦〉 ∣ (𝑥 ∈ 𝐴 ∧ 𝑦 = 𝐵)} | 
| 15 |   | df-mpt 4096 | 
. 2
⊢ (𝑥 ∈ 𝐶 ↦ 𝐷) = {〈𝑥, 𝑦〉 ∣ (𝑥 ∈ 𝐶 ∧ 𝑦 = 𝐷)} | 
| 16 | 13, 14, 15 | 3eqtr4g 2254 | 
1
⊢
((∀𝑥 𝐴 = 𝐶 ∧ ∀𝑥 ∈ 𝐴 𝐵 = 𝐷) → (𝑥 ∈ 𝐴 ↦ 𝐵) = (𝑥 ∈ 𝐶 ↦ 𝐷)) |