| Step | Hyp | Ref
| Expression |
| 1 | | nfv 1914 |
. . . . 5
⊢
Ⅎ𝑎 𝐴 ∈ 𝑋 |
| 2 | | nfv 1914 |
. . . . 5
⊢
Ⅎ𝑎 𝐵 ∈ 𝑋 |
| 3 | | nfich1 47428 |
. . . . 5
⊢
Ⅎ𝑎[𝑎⇄𝑏]𝜑 |
| 4 | 1, 2, 3 | nf3an 1901 |
. . . 4
⊢
Ⅎ𝑎(𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) |
| 5 | | nfv 1914 |
. . . . . . 7
⊢
Ⅎ𝑎〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 |
| 6 | | nfcv 2899 |
. . . . . . . 8
⊢
Ⅎ𝑎𝑦 |
| 7 | | nfsbc1v 3790 |
. . . . . . . 8
⊢
Ⅎ𝑎[𝑥 / 𝑎]𝜑 |
| 8 | 6, 7 | nfsbcw 3792 |
. . . . . . 7
⊢
Ⅎ𝑎[𝑦 / 𝑏][𝑥 / 𝑎]𝜑 |
| 9 | 5, 8 | nfan 1899 |
. . . . . 6
⊢
Ⅎ𝑎(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑) |
| 10 | 9 | nfex 2325 |
. . . . 5
⊢
Ⅎ𝑎∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑) |
| 11 | 10 | nfex 2325 |
. . . 4
⊢
Ⅎ𝑎∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑) |
| 12 | | nfv 1914 |
. . . . . 6
⊢
Ⅎ𝑏 𝐴 ∈ 𝑋 |
| 13 | | nfv 1914 |
. . . . . 6
⊢
Ⅎ𝑏 𝐵 ∈ 𝑋 |
| 14 | | nfich2 47429 |
. . . . . 6
⊢
Ⅎ𝑏[𝑎⇄𝑏]𝜑 |
| 15 | 12, 13, 14 | nf3an 1901 |
. . . . 5
⊢
Ⅎ𝑏(𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) |
| 16 | | nfv 1914 |
. . . . . . . 8
⊢
Ⅎ𝑏〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 |
| 17 | | nfsbc1v 3790 |
. . . . . . . 8
⊢
Ⅎ𝑏[𝑦 / 𝑏][𝑥 / 𝑎]𝜑 |
| 18 | 16, 17 | nfan 1899 |
. . . . . . 7
⊢
Ⅎ𝑏(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑) |
| 19 | 18 | nfex 2325 |
. . . . . 6
⊢
Ⅎ𝑏∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑) |
| 20 | 19 | nfex 2325 |
. . . . 5
⊢
Ⅎ𝑏∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑) |
| 21 | | vex 3468 |
. . . . . . . . 9
⊢ 𝑎 ∈ V |
| 22 | | vex 3468 |
. . . . . . . . 9
⊢ 𝑏 ∈ V |
| 23 | | preq12bg 4834 |
. . . . . . . . 9
⊢ (((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋) ∧ (𝑎 ∈ V ∧ 𝑏 ∈ V)) → ({𝐴, 𝐵} = {𝑎, 𝑏} ↔ ((𝐴 = 𝑎 ∧ 𝐵 = 𝑏) ∨ (𝐴 = 𝑏 ∧ 𝐵 = 𝑎)))) |
| 24 | 21, 22, 23 | mpanr12 705 |
. . . . . . . 8
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋) → ({𝐴, 𝐵} = {𝑎, 𝑏} ↔ ((𝐴 = 𝑎 ∧ 𝐵 = 𝑏) ∨ (𝐴 = 𝑏 ∧ 𝐵 = 𝑎)))) |
| 25 | 24 | 3adant3 1132 |
. . . . . . 7
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) → ({𝐴, 𝐵} = {𝑎, 𝑏} ↔ ((𝐴 = 𝑎 ∧ 𝐵 = 𝑏) ∨ (𝐴 = 𝑏 ∧ 𝐵 = 𝑎)))) |
| 26 | | or2expropbilem1 47028 |
. . . . . . . . 9
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋) → ((𝐴 = 𝑎 ∧ 𝐵 = 𝑏) → (𝜑 → ∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑)))) |
| 27 | 26 | 3adant3 1132 |
. . . . . . . 8
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) → ((𝐴 = 𝑎 ∧ 𝐵 = 𝑏) → (𝜑 → ∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑)))) |
| 28 | | ichcom 47440 |
. . . . . . . . . . . . . . 15
⊢ ([𝑎⇄𝑏]𝜑 ↔ [𝑏⇄𝑎]𝜑) |
| 29 | 28 | biimpi 216 |
. . . . . . . . . . . . . 14
⊢ ([𝑎⇄𝑏]𝜑 → [𝑏⇄𝑎]𝜑) |
| 30 | 29 | 3ad2ant3 1135 |
. . . . . . . . . . . . 13
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) → [𝑏⇄𝑎]𝜑) |
| 31 | 30 | adantr 480 |
. . . . . . . . . . . 12
⊢ (((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) ∧ 𝜑) → [𝑏⇄𝑎]𝜑) |
| 32 | 22, 21 | pm3.2i 470 |
. . . . . . . . . . . . 13
⊢ (𝑏 ∈ V ∧ 𝑎 ∈ V) |
| 33 | 32 | a1i 11 |
. . . . . . . . . . . 12
⊢ ((𝐴 = 𝑏 ∧ 𝐵 = 𝑎) → (𝑏 ∈ V ∧ 𝑎 ∈ V)) |
| 34 | 31, 33 | anim12i 613 |
. . . . . . . . . . 11
⊢ ((((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) ∧ 𝜑) ∧ (𝐴 = 𝑏 ∧ 𝐵 = 𝑎)) → ([𝑏⇄𝑎]𝜑 ∧ (𝑏 ∈ V ∧ 𝑎 ∈ V))) |
| 35 | | simpr 484 |
. . . . . . . . . . . 12
⊢ (((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) ∧ 𝜑) → 𝜑) |
| 36 | | opeq12 4856 |
. . . . . . . . . . . 12
⊢ ((𝐴 = 𝑏 ∧ 𝐵 = 𝑎) → 〈𝐴, 𝐵〉 = 〈𝑏, 𝑎〉) |
| 37 | 35, 36 | anim12ci 614 |
. . . . . . . . . . 11
⊢ ((((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) ∧ 𝜑) ∧ (𝐴 = 𝑏 ∧ 𝐵 = 𝑎)) → (〈𝐴, 𝐵〉 = 〈𝑏, 𝑎〉 ∧ 𝜑)) |
| 38 | | nfv 1914 |
. . . . . . . . . . . 12
⊢
Ⅎ𝑥(〈𝐴, 𝐵〉 = 〈𝑏, 𝑎〉 ∧ 𝜑) |
| 39 | | nfv 1914 |
. . . . . . . . . . . 12
⊢
Ⅎ𝑦(〈𝐴, 𝐵〉 = 〈𝑏, 𝑎〉 ∧ 𝜑) |
| 40 | | opeq12 4856 |
. . . . . . . . . . . . . . 15
⊢ ((𝑥 = 𝑏 ∧ 𝑦 = 𝑎) → 〈𝑥, 𝑦〉 = 〈𝑏, 𝑎〉) |
| 41 | 40 | eqeq2d 2747 |
. . . . . . . . . . . . . 14
⊢ ((𝑥 = 𝑏 ∧ 𝑦 = 𝑎) → (〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ↔ 〈𝐴, 𝐵〉 = 〈𝑏, 𝑎〉)) |
| 42 | 41 | adantl 481 |
. . . . . . . . . . . . 13
⊢ (([𝑏⇄𝑎]𝜑 ∧ (𝑥 = 𝑏 ∧ 𝑦 = 𝑎)) → (〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ↔ 〈𝐴, 𝐵〉 = 〈𝑏, 𝑎〉)) |
| 43 | | dfsbcq 3772 |
. . . . . . . . . . . . . . . 16
⊢ (𝑦 = 𝑎 → ([𝑦 / 𝑏][𝑥 / 𝑎]𝜑 ↔ [𝑎 / 𝑏][𝑥 / 𝑎]𝜑)) |
| 44 | 43 | adantl 481 |
. . . . . . . . . . . . . . 15
⊢ ((𝑥 = 𝑏 ∧ 𝑦 = 𝑎) → ([𝑦 / 𝑏][𝑥 / 𝑎]𝜑 ↔ [𝑎 / 𝑏][𝑥 / 𝑎]𝜑)) |
| 45 | 44 | adantl 481 |
. . . . . . . . . . . . . 14
⊢ (([𝑏⇄𝑎]𝜑 ∧ (𝑥 = 𝑏 ∧ 𝑦 = 𝑎)) → ([𝑦 / 𝑏][𝑥 / 𝑎]𝜑 ↔ [𝑎 / 𝑏][𝑥 / 𝑎]𝜑)) |
| 46 | | sbceq1a 3781 |
. . . . . . . . . . . . . . . 16
⊢ (𝑥 = 𝑏 → ([𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ [𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑)) |
| 47 | 46 | adantr 480 |
. . . . . . . . . . . . . . 15
⊢ ((𝑥 = 𝑏 ∧ 𝑦 = 𝑎) → ([𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ [𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑)) |
| 48 | | df-ich 47427 |
. . . . . . . . . . . . . . . 16
⊢ ([𝑏⇄𝑎]𝜑 ↔ ∀𝑏∀𝑎([𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ 𝜑)) |
| 49 | | sbsbc 3774 |
. . . . . . . . . . . . . . . . . 18
⊢ ([𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ [𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑) |
| 50 | | sbsbc 3774 |
. . . . . . . . . . . . . . . . . . . 20
⊢ ([𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ [𝑎 / 𝑏][𝑥 / 𝑎]𝜑) |
| 51 | | sbsbc 3774 |
. . . . . . . . . . . . . . . . . . . . 21
⊢ ([𝑥 / 𝑎]𝜑 ↔ [𝑥 / 𝑎]𝜑) |
| 52 | 51 | sbcbii 3827 |
. . . . . . . . . . . . . . . . . . . 20
⊢
([𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ [𝑎 / 𝑏][𝑥 / 𝑎]𝜑) |
| 53 | 50, 52 | bitri 275 |
. . . . . . . . . . . . . . . . . . 19
⊢ ([𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ [𝑎 / 𝑏][𝑥 / 𝑎]𝜑) |
| 54 | 53 | sbcbii 3827 |
. . . . . . . . . . . . . . . . . 18
⊢
([𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ [𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑) |
| 55 | 49, 54 | bitri 275 |
. . . . . . . . . . . . . . . . 17
⊢ ([𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ [𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑) |
| 56 | | 2sp 2187 |
. . . . . . . . . . . . . . . . 17
⊢
(∀𝑏∀𝑎([𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ 𝜑) → ([𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ 𝜑)) |
| 57 | 55, 56 | bitr3id 285 |
. . . . . . . . . . . . . . . 16
⊢
(∀𝑏∀𝑎([𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ 𝜑) → ([𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ 𝜑)) |
| 58 | 48, 57 | sylbi 217 |
. . . . . . . . . . . . . . 15
⊢ ([𝑏⇄𝑎]𝜑 → ([𝑏 / 𝑥][𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ 𝜑)) |
| 59 | 47, 58 | sylan9bbr 510 |
. . . . . . . . . . . . . 14
⊢ (([𝑏⇄𝑎]𝜑 ∧ (𝑥 = 𝑏 ∧ 𝑦 = 𝑎)) → ([𝑎 / 𝑏][𝑥 / 𝑎]𝜑 ↔ 𝜑)) |
| 60 | 45, 59 | bitrd 279 |
. . . . . . . . . . . . 13
⊢ (([𝑏⇄𝑎]𝜑 ∧ (𝑥 = 𝑏 ∧ 𝑦 = 𝑎)) → ([𝑦 / 𝑏][𝑥 / 𝑎]𝜑 ↔ 𝜑)) |
| 61 | 42, 60 | anbi12d 632 |
. . . . . . . . . . . 12
⊢ (([𝑏⇄𝑎]𝜑 ∧ (𝑥 = 𝑏 ∧ 𝑦 = 𝑎)) → ((〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑) ↔ (〈𝐴, 𝐵〉 = 〈𝑏, 𝑎〉 ∧ 𝜑))) |
| 62 | 38, 39, 61 | spc2ed 3585 |
. . . . . . . . . . 11
⊢ (([𝑏⇄𝑎]𝜑 ∧ (𝑏 ∈ V ∧ 𝑎 ∈ V)) → ((〈𝐴, 𝐵〉 = 〈𝑏, 𝑎〉 ∧ 𝜑) → ∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑))) |
| 63 | 34, 37, 62 | sylc 65 |
. . . . . . . . . 10
⊢ ((((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) ∧ 𝜑) ∧ (𝐴 = 𝑏 ∧ 𝐵 = 𝑎)) → ∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑)) |
| 64 | 63 | exp31 419 |
. . . . . . . . 9
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) → (𝜑 → ((𝐴 = 𝑏 ∧ 𝐵 = 𝑎) → ∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑)))) |
| 65 | 64 | com23 86 |
. . . . . . . 8
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) → ((𝐴 = 𝑏 ∧ 𝐵 = 𝑎) → (𝜑 → ∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑)))) |
| 66 | 27, 65 | jaod 859 |
. . . . . . 7
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) → (((𝐴 = 𝑎 ∧ 𝐵 = 𝑏) ∨ (𝐴 = 𝑏 ∧ 𝐵 = 𝑎)) → (𝜑 → ∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑)))) |
| 67 | 25, 66 | sylbid 240 |
. . . . . 6
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) → ({𝐴, 𝐵} = {𝑎, 𝑏} → (𝜑 → ∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑)))) |
| 68 | 67 | impd 410 |
. . . . 5
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) → (({𝐴, 𝐵} = {𝑎, 𝑏} ∧ 𝜑) → ∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑))) |
| 69 | 15, 20, 68 | exlimd 2219 |
. . . 4
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) → (∃𝑏({𝐴, 𝐵} = {𝑎, 𝑏} ∧ 𝜑) → ∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑))) |
| 70 | 4, 11, 69 | exlimd 2219 |
. . 3
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) → (∃𝑎∃𝑏({𝐴, 𝐵} = {𝑎, 𝑏} ∧ 𝜑) → ∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑))) |
| 71 | | or2expropbilem2 47029 |
. . 3
⊢
(∃𝑎∃𝑏(〈𝐴, 𝐵〉 = 〈𝑎, 𝑏〉 ∧ 𝜑) ↔ ∃𝑥∃𝑦(〈𝐴, 𝐵〉 = 〈𝑥, 𝑦〉 ∧ [𝑦 / 𝑏][𝑥 / 𝑎]𝜑)) |
| 72 | 70, 71 | imbitrrdi 252 |
. 2
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) → (∃𝑎∃𝑏({𝐴, 𝐵} = {𝑎, 𝑏} ∧ 𝜑) → ∃𝑎∃𝑏(〈𝐴, 𝐵〉 = 〈𝑎, 𝑏〉 ∧ 𝜑))) |
| 73 | | oppr 47026 |
. . . . 5
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋) → (〈𝐴, 𝐵〉 = 〈𝑎, 𝑏〉 → {𝐴, 𝐵} = {𝑎, 𝑏})) |
| 74 | 73 | anim1d 611 |
. . . 4
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋) → ((〈𝐴, 𝐵〉 = 〈𝑎, 𝑏〉 ∧ 𝜑) → ({𝐴, 𝐵} = {𝑎, 𝑏} ∧ 𝜑))) |
| 75 | 74 | 2eximdv 1919 |
. . 3
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋) → (∃𝑎∃𝑏(〈𝐴, 𝐵〉 = 〈𝑎, 𝑏〉 ∧ 𝜑) → ∃𝑎∃𝑏({𝐴, 𝐵} = {𝑎, 𝑏} ∧ 𝜑))) |
| 76 | 75 | 3adant3 1132 |
. 2
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) → (∃𝑎∃𝑏(〈𝐴, 𝐵〉 = 〈𝑎, 𝑏〉 ∧ 𝜑) → ∃𝑎∃𝑏({𝐴, 𝐵} = {𝑎, 𝑏} ∧ 𝜑))) |
| 77 | 72, 76 | impbid 212 |
1
⊢ ((𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ [𝑎⇄𝑏]𝜑) → (∃𝑎∃𝑏({𝐴, 𝐵} = {𝑎, 𝑏} ∧ 𝜑) ↔ ∃𝑎∃𝑏(〈𝐴, 𝐵〉 = 〈𝑎, 𝑏〉 ∧ 𝜑))) |