Step | Hyp | Ref
| Expression |
1 | | ssid 3939 |
. 2
⊢ 𝐴 ⊆ 𝐴 |
2 | | fsum2d.2 |
. . 3
⊢ (𝜑 → 𝐴 ∈ Fin) |
3 | | sseq1 3942 |
. . . . . 6
⊢ (𝑤 = ∅ → (𝑤 ⊆ 𝐴 ↔ ∅ ⊆ 𝐴)) |
4 | | sumeq1 15328 |
. . . . . . 7
⊢ (𝑤 = ∅ → Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑗 ∈ ∅ Σ𝑘 ∈ 𝐵 𝐶) |
5 | | iuneq1 4937 |
. . . . . . . 8
⊢ (𝑤 = ∅ → ∪ 𝑗 ∈ 𝑤 ({𝑗} × 𝐵) = ∪
𝑗 ∈ ∅ ({𝑗} × 𝐵)) |
6 | 5 | sumeq1d 15341 |
. . . . . . 7
⊢ (𝑤 = ∅ → Σ𝑧 ∈ ∪ 𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷 = Σ𝑧 ∈ ∪
𝑗 ∈ ∅ ({𝑗} × 𝐵)𝐷) |
7 | 4, 6 | eqeq12d 2754 |
. . . . . 6
⊢ (𝑤 = ∅ → (Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷 ↔ Σ𝑗 ∈ ∅ Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ ∅ ({𝑗} × 𝐵)𝐷)) |
8 | 3, 7 | imbi12d 344 |
. . . . 5
⊢ (𝑤 = ∅ → ((𝑤 ⊆ 𝐴 → Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷) ↔ (∅ ⊆ 𝐴 → Σ𝑗 ∈ ∅ Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ ∅ ({𝑗} × 𝐵)𝐷))) |
9 | 8 | imbi2d 340 |
. . . 4
⊢ (𝑤 = ∅ → ((𝜑 → (𝑤 ⊆ 𝐴 → Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷)) ↔ (𝜑 → (∅ ⊆ 𝐴 → Σ𝑗 ∈ ∅ Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ ∅ ({𝑗} × 𝐵)𝐷)))) |
10 | | sseq1 3942 |
. . . . . 6
⊢ (𝑤 = 𝑥 → (𝑤 ⊆ 𝐴 ↔ 𝑥 ⊆ 𝐴)) |
11 | | sumeq1 15328 |
. . . . . . 7
⊢ (𝑤 = 𝑥 → Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶) |
12 | | iuneq1 4937 |
. . . . . . . 8
⊢ (𝑤 = 𝑥 → ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵) = ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)) |
13 | 12 | sumeq1d 15341 |
. . . . . . 7
⊢ (𝑤 = 𝑥 → Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷) |
14 | 11, 13 | eqeq12d 2754 |
. . . . . 6
⊢ (𝑤 = 𝑥 → (Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷 ↔ Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷)) |
15 | 10, 14 | imbi12d 344 |
. . . . 5
⊢ (𝑤 = 𝑥 → ((𝑤 ⊆ 𝐴 → Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷) ↔ (𝑥 ⊆ 𝐴 → Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷))) |
16 | 15 | imbi2d 340 |
. . . 4
⊢ (𝑤 = 𝑥 → ((𝜑 → (𝑤 ⊆ 𝐴 → Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷)) ↔ (𝜑 → (𝑥 ⊆ 𝐴 → Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷)))) |
17 | | sseq1 3942 |
. . . . . 6
⊢ (𝑤 = (𝑥 ∪ {𝑦}) → (𝑤 ⊆ 𝐴 ↔ (𝑥 ∪ {𝑦}) ⊆ 𝐴)) |
18 | | sumeq1 15328 |
. . . . . . 7
⊢ (𝑤 = (𝑥 ∪ {𝑦}) → Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑗 ∈ (𝑥 ∪ {𝑦})Σ𝑘 ∈ 𝐵 𝐶) |
19 | | iuneq1 4937 |
. . . . . . . 8
⊢ (𝑤 = (𝑥 ∪ {𝑦}) → ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵) = ∪
𝑗 ∈ (𝑥 ∪ {𝑦})({𝑗} × 𝐵)) |
20 | 19 | sumeq1d 15341 |
. . . . . . 7
⊢ (𝑤 = (𝑥 ∪ {𝑦}) → Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷 = Σ𝑧 ∈ ∪
𝑗 ∈ (𝑥 ∪ {𝑦})({𝑗} × 𝐵)𝐷) |
21 | 18, 20 | eqeq12d 2754 |
. . . . . 6
⊢ (𝑤 = (𝑥 ∪ {𝑦}) → (Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷 ↔ Σ𝑗 ∈ (𝑥 ∪ {𝑦})Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ (𝑥 ∪ {𝑦})({𝑗} × 𝐵)𝐷)) |
22 | 17, 21 | imbi12d 344 |
. . . . 5
⊢ (𝑤 = (𝑥 ∪ {𝑦}) → ((𝑤 ⊆ 𝐴 → Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷) ↔ ((𝑥 ∪ {𝑦}) ⊆ 𝐴 → Σ𝑗 ∈ (𝑥 ∪ {𝑦})Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ (𝑥 ∪ {𝑦})({𝑗} × 𝐵)𝐷))) |
23 | 22 | imbi2d 340 |
. . . 4
⊢ (𝑤 = (𝑥 ∪ {𝑦}) → ((𝜑 → (𝑤 ⊆ 𝐴 → Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷)) ↔ (𝜑 → ((𝑥 ∪ {𝑦}) ⊆ 𝐴 → Σ𝑗 ∈ (𝑥 ∪ {𝑦})Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ (𝑥 ∪ {𝑦})({𝑗} × 𝐵)𝐷)))) |
24 | | sseq1 3942 |
. . . . . 6
⊢ (𝑤 = 𝐴 → (𝑤 ⊆ 𝐴 ↔ 𝐴 ⊆ 𝐴)) |
25 | | sumeq1 15328 |
. . . . . . 7
⊢ (𝑤 = 𝐴 → Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑗 ∈ 𝐴 Σ𝑘 ∈ 𝐵 𝐶) |
26 | | iuneq1 4937 |
. . . . . . . 8
⊢ (𝑤 = 𝐴 → ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵) = ∪
𝑗 ∈ 𝐴 ({𝑗} × 𝐵)) |
27 | 26 | sumeq1d 15341 |
. . . . . . 7
⊢ (𝑤 = 𝐴 → Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝐴 ({𝑗} × 𝐵)𝐷) |
28 | 25, 27 | eqeq12d 2754 |
. . . . . 6
⊢ (𝑤 = 𝐴 → (Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷 ↔ Σ𝑗 ∈ 𝐴 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝐴 ({𝑗} × 𝐵)𝐷)) |
29 | 24, 28 | imbi12d 344 |
. . . . 5
⊢ (𝑤 = 𝐴 → ((𝑤 ⊆ 𝐴 → Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷) ↔ (𝐴 ⊆ 𝐴 → Σ𝑗 ∈ 𝐴 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝐴 ({𝑗} × 𝐵)𝐷))) |
30 | 29 | imbi2d 340 |
. . . 4
⊢ (𝑤 = 𝐴 → ((𝜑 → (𝑤 ⊆ 𝐴 → Σ𝑗 ∈ 𝑤 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑤 ({𝑗} × 𝐵)𝐷)) ↔ (𝜑 → (𝐴 ⊆ 𝐴 → Σ𝑗 ∈ 𝐴 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝐴 ({𝑗} × 𝐵)𝐷)))) |
31 | | sum0 15361 |
. . . . . 6
⊢
Σ𝑧 ∈
∅ 𝐷 =
0 |
32 | | 0iun 4988 |
. . . . . . 7
⊢ ∪ 𝑗 ∈ ∅ ({𝑗} × 𝐵) = ∅ |
33 | 32 | sumeq1i 15338 |
. . . . . 6
⊢
Σ𝑧 ∈
∪ 𝑗 ∈ ∅ ({𝑗} × 𝐵)𝐷 = Σ𝑧 ∈ ∅ 𝐷 |
34 | | sum0 15361 |
. . . . . 6
⊢
Σ𝑗 ∈
∅ Σ𝑘 ∈
𝐵 𝐶 = 0 |
35 | 31, 33, 34 | 3eqtr4ri 2777 |
. . . . 5
⊢
Σ𝑗 ∈
∅ Σ𝑘 ∈
𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ ∅ ({𝑗} × 𝐵)𝐷 |
36 | 35 | 2a1i 12 |
. . . 4
⊢ (𝜑 → (∅ ⊆ 𝐴 → Σ𝑗 ∈ ∅ Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ ∅ ({𝑗} × 𝐵)𝐷)) |
37 | | ssun1 4102 |
. . . . . . . . . 10
⊢ 𝑥 ⊆ (𝑥 ∪ {𝑦}) |
38 | | sstr 3925 |
. . . . . . . . . 10
⊢ ((𝑥 ⊆ (𝑥 ∪ {𝑦}) ∧ (𝑥 ∪ {𝑦}) ⊆ 𝐴) → 𝑥 ⊆ 𝐴) |
39 | 37, 38 | mpan 686 |
. . . . . . . . 9
⊢ ((𝑥 ∪ {𝑦}) ⊆ 𝐴 → 𝑥 ⊆ 𝐴) |
40 | 39 | imim1i 63 |
. . . . . . . 8
⊢ ((𝑥 ⊆ 𝐴 → Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷) → ((𝑥 ∪ {𝑦}) ⊆ 𝐴 → Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷)) |
41 | | fsum2d.1 |
. . . . . . . . . . 11
⊢ (𝑧 = 〈𝑗, 𝑘〉 → 𝐷 = 𝐶) |
42 | | simpll 763 |
. . . . . . . . . . . 12
⊢ (((𝜑 ∧ ¬ 𝑦 ∈ 𝑥) ∧ (𝑥 ∪ {𝑦}) ⊆ 𝐴) → 𝜑) |
43 | 42, 2 | syl 17 |
. . . . . . . . . . 11
⊢ (((𝜑 ∧ ¬ 𝑦 ∈ 𝑥) ∧ (𝑥 ∪ {𝑦}) ⊆ 𝐴) → 𝐴 ∈ Fin) |
44 | | fsum2d.3 |
. . . . . . . . . . . 12
⊢ ((𝜑 ∧ 𝑗 ∈ 𝐴) → 𝐵 ∈ Fin) |
45 | 42, 44 | sylan 579 |
. . . . . . . . . . 11
⊢ ((((𝜑 ∧ ¬ 𝑦 ∈ 𝑥) ∧ (𝑥 ∪ {𝑦}) ⊆ 𝐴) ∧ 𝑗 ∈ 𝐴) → 𝐵 ∈ Fin) |
46 | | fsum2d.4 |
. . . . . . . . . . . 12
⊢ ((𝜑 ∧ (𝑗 ∈ 𝐴 ∧ 𝑘 ∈ 𝐵)) → 𝐶 ∈ ℂ) |
47 | 42, 46 | sylan 579 |
. . . . . . . . . . 11
⊢ ((((𝜑 ∧ ¬ 𝑦 ∈ 𝑥) ∧ (𝑥 ∪ {𝑦}) ⊆ 𝐴) ∧ (𝑗 ∈ 𝐴 ∧ 𝑘 ∈ 𝐵)) → 𝐶 ∈ ℂ) |
48 | | simplr 765 |
. . . . . . . . . . 11
⊢ (((𝜑 ∧ ¬ 𝑦 ∈ 𝑥) ∧ (𝑥 ∪ {𝑦}) ⊆ 𝐴) → ¬ 𝑦 ∈ 𝑥) |
49 | | simpr 484 |
. . . . . . . . . . 11
⊢ (((𝜑 ∧ ¬ 𝑦 ∈ 𝑥) ∧ (𝑥 ∪ {𝑦}) ⊆ 𝐴) → (𝑥 ∪ {𝑦}) ⊆ 𝐴) |
50 | | biid 260 |
. . . . . . . . . . 11
⊢
(Σ𝑗 ∈
𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷 ↔ Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷) |
51 | 41, 43, 45, 47, 48, 49, 50 | fsum2dlem 15410 |
. . . . . . . . . 10
⊢ ((((𝜑 ∧ ¬ 𝑦 ∈ 𝑥) ∧ (𝑥 ∪ {𝑦}) ⊆ 𝐴) ∧ Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷) → Σ𝑗 ∈ (𝑥 ∪ {𝑦})Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ (𝑥 ∪ {𝑦})({𝑗} × 𝐵)𝐷) |
52 | 51 | exp31 419 |
. . . . . . . . 9
⊢ ((𝜑 ∧ ¬ 𝑦 ∈ 𝑥) → ((𝑥 ∪ {𝑦}) ⊆ 𝐴 → (Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷 → Σ𝑗 ∈ (𝑥 ∪ {𝑦})Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ (𝑥 ∪ {𝑦})({𝑗} × 𝐵)𝐷))) |
53 | 52 | a2d 29 |
. . . . . . . 8
⊢ ((𝜑 ∧ ¬ 𝑦 ∈ 𝑥) → (((𝑥 ∪ {𝑦}) ⊆ 𝐴 → Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷) → ((𝑥 ∪ {𝑦}) ⊆ 𝐴 → Σ𝑗 ∈ (𝑥 ∪ {𝑦})Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ (𝑥 ∪ {𝑦})({𝑗} × 𝐵)𝐷))) |
54 | 40, 53 | syl5 34 |
. . . . . . 7
⊢ ((𝜑 ∧ ¬ 𝑦 ∈ 𝑥) → ((𝑥 ⊆ 𝐴 → Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷) → ((𝑥 ∪ {𝑦}) ⊆ 𝐴 → Σ𝑗 ∈ (𝑥 ∪ {𝑦})Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ (𝑥 ∪ {𝑦})({𝑗} × 𝐵)𝐷))) |
55 | 54 | expcom 413 |
. . . . . 6
⊢ (¬
𝑦 ∈ 𝑥 → (𝜑 → ((𝑥 ⊆ 𝐴 → Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷) → ((𝑥 ∪ {𝑦}) ⊆ 𝐴 → Σ𝑗 ∈ (𝑥 ∪ {𝑦})Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ (𝑥 ∪ {𝑦})({𝑗} × 𝐵)𝐷)))) |
56 | 55 | a2d 29 |
. . . . 5
⊢ (¬
𝑦 ∈ 𝑥 → ((𝜑 → (𝑥 ⊆ 𝐴 → Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷)) → (𝜑 → ((𝑥 ∪ {𝑦}) ⊆ 𝐴 → Σ𝑗 ∈ (𝑥 ∪ {𝑦})Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ (𝑥 ∪ {𝑦})({𝑗} × 𝐵)𝐷)))) |
57 | 56 | adantl 481 |
. . . 4
⊢ ((𝑥 ∈ Fin ∧ ¬ 𝑦 ∈ 𝑥) → ((𝜑 → (𝑥 ⊆ 𝐴 → Σ𝑗 ∈ 𝑥 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝑥 ({𝑗} × 𝐵)𝐷)) → (𝜑 → ((𝑥 ∪ {𝑦}) ⊆ 𝐴 → Σ𝑗 ∈ (𝑥 ∪ {𝑦})Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ (𝑥 ∪ {𝑦})({𝑗} × 𝐵)𝐷)))) |
58 | 9, 16, 23, 30, 36, 57 | findcard2s 8910 |
. . 3
⊢ (𝐴 ∈ Fin → (𝜑 → (𝐴 ⊆ 𝐴 → Σ𝑗 ∈ 𝐴 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝐴 ({𝑗} × 𝐵)𝐷))) |
59 | 2, 58 | mpcom 38 |
. 2
⊢ (𝜑 → (𝐴 ⊆ 𝐴 → Σ𝑗 ∈ 𝐴 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝐴 ({𝑗} × 𝐵)𝐷)) |
60 | 1, 59 | mpi 20 |
1
⊢ (𝜑 → Σ𝑗 ∈ 𝐴 Σ𝑘 ∈ 𝐵 𝐶 = Σ𝑧 ∈ ∪
𝑗 ∈ 𝐴 ({𝑗} × 𝐵)𝐷) |