Proof of Theorem dvfsumge
| Step | Hyp | Ref
| Expression |
| 1 | | dvfsumleOLD.m |
. . . 4
⊢ (𝜑 → 𝑁 ∈ (ℤ≥‘𝑀)) |
| 2 | | df-neg 11474 |
. . . . . 6
⊢ -𝐴 = (0 − 𝐴) |
| 3 | 2 | mpteq2i 5222 |
. . . . 5
⊢ (𝑥 ∈ (𝑀[,]𝑁) ↦ -𝐴) = (𝑥 ∈ (𝑀[,]𝑁) ↦ (0 − 𝐴)) |
| 4 | | eqid 2736 |
. . . . . 6
⊢
(TopOpen‘ℂfld) =
(TopOpen‘ℂfld) |
| 5 | 4 | subcn 24811 |
. . . . . 6
⊢ −
∈ (((TopOpen‘ℂfld) ×t
(TopOpen‘ℂfld)) Cn
(TopOpen‘ℂfld)) |
| 6 | | 0red 11243 |
. . . . . . 7
⊢ (𝜑 → 0 ∈
ℝ) |
| 7 | | eluzel2 12862 |
. . . . . . . . . . 11
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → 𝑀 ∈ ℤ) |
| 8 | 1, 7 | syl 17 |
. . . . . . . . . 10
⊢ (𝜑 → 𝑀 ∈ ℤ) |
| 9 | 8 | zred 12702 |
. . . . . . . . 9
⊢ (𝜑 → 𝑀 ∈ ℝ) |
| 10 | | eluzelz 12867 |
. . . . . . . . . . 11
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → 𝑁 ∈ ℤ) |
| 11 | 1, 10 | syl 17 |
. . . . . . . . . 10
⊢ (𝜑 → 𝑁 ∈ ℤ) |
| 12 | 11 | zred 12702 |
. . . . . . . . 9
⊢ (𝜑 → 𝑁 ∈ ℝ) |
| 13 | | iccssre 13451 |
. . . . . . . . 9
⊢ ((𝑀 ∈ ℝ ∧ 𝑁 ∈ ℝ) → (𝑀[,]𝑁) ⊆ ℝ) |
| 14 | 9, 12, 13 | syl2anc 584 |
. . . . . . . 8
⊢ (𝜑 → (𝑀[,]𝑁) ⊆ ℝ) |
| 15 | | ax-resscn 11191 |
. . . . . . . 8
⊢ ℝ
⊆ ℂ |
| 16 | 14, 15 | sstrdi 3976 |
. . . . . . 7
⊢ (𝜑 → (𝑀[,]𝑁) ⊆ ℂ) |
| 17 | 15 | a1i 11 |
. . . . . . 7
⊢ (𝜑 → ℝ ⊆
ℂ) |
| 18 | | cncfmptc 24861 |
. . . . . . 7
⊢ ((0
∈ ℝ ∧ (𝑀[,]𝑁) ⊆ ℂ ∧ ℝ ⊆
ℂ) → (𝑥 ∈
(𝑀[,]𝑁) ↦ 0) ∈ ((𝑀[,]𝑁)–cn→ℝ)) |
| 19 | 6, 16, 17, 18 | syl3anc 1373 |
. . . . . 6
⊢ (𝜑 → (𝑥 ∈ (𝑀[,]𝑁) ↦ 0) ∈ ((𝑀[,]𝑁)–cn→ℝ)) |
| 20 | | dvfsumleOLD.a |
. . . . . 6
⊢ (𝜑 → (𝑥 ∈ (𝑀[,]𝑁) ↦ 𝐴) ∈ ((𝑀[,]𝑁)–cn→ℝ)) |
| 21 | | resubcl 11552 |
. . . . . 6
⊢ ((0
∈ ℝ ∧ 𝐴
∈ ℝ) → (0 − 𝐴) ∈ ℝ) |
| 22 | 4, 5, 19, 20, 15, 21 | cncfmpt2ss 24865 |
. . . . 5
⊢ (𝜑 → (𝑥 ∈ (𝑀[,]𝑁) ↦ (0 − 𝐴)) ∈ ((𝑀[,]𝑁)–cn→ℝ)) |
| 23 | 3, 22 | eqeltrid 2839 |
. . . 4
⊢ (𝜑 → (𝑥 ∈ (𝑀[,]𝑁) ↦ -𝐴) ∈ ((𝑀[,]𝑁)–cn→ℝ)) |
| 24 | | negex 11485 |
. . . . 5
⊢ -𝐵 ∈ V |
| 25 | 24 | a1i 11 |
. . . 4
⊢ ((𝜑 ∧ 𝑥 ∈ (𝑀(,)𝑁)) → -𝐵 ∈ V) |
| 26 | | reelprrecn 11226 |
. . . . . 6
⊢ ℝ
∈ {ℝ, ℂ} |
| 27 | 26 | a1i 11 |
. . . . 5
⊢ (𝜑 → ℝ ∈ {ℝ,
ℂ}) |
| 28 | | ioossicc 13455 |
. . . . . . . 8
⊢ (𝑀(,)𝑁) ⊆ (𝑀[,]𝑁) |
| 29 | 28 | sseli 3959 |
. . . . . . 7
⊢ (𝑥 ∈ (𝑀(,)𝑁) → 𝑥 ∈ (𝑀[,]𝑁)) |
| 30 | | cncff 24842 |
. . . . . . . . 9
⊢ ((𝑥 ∈ (𝑀[,]𝑁) ↦ 𝐴) ∈ ((𝑀[,]𝑁)–cn→ℝ) → (𝑥 ∈ (𝑀[,]𝑁) ↦ 𝐴):(𝑀[,]𝑁)⟶ℝ) |
| 31 | 20, 30 | syl 17 |
. . . . . . . 8
⊢ (𝜑 → (𝑥 ∈ (𝑀[,]𝑁) ↦ 𝐴):(𝑀[,]𝑁)⟶ℝ) |
| 32 | 31 | fvmptelcdm 7108 |
. . . . . . 7
⊢ ((𝜑 ∧ 𝑥 ∈ (𝑀[,]𝑁)) → 𝐴 ∈ ℝ) |
| 33 | 29, 32 | sylan2 593 |
. . . . . 6
⊢ ((𝜑 ∧ 𝑥 ∈ (𝑀(,)𝑁)) → 𝐴 ∈ ℝ) |
| 34 | 33 | recnd 11268 |
. . . . 5
⊢ ((𝜑 ∧ 𝑥 ∈ (𝑀(,)𝑁)) → 𝐴 ∈ ℂ) |
| 35 | | dvfsumleOLD.v |
. . . . 5
⊢ ((𝜑 ∧ 𝑥 ∈ (𝑀(,)𝑁)) → 𝐵 ∈ 𝑉) |
| 36 | | dvfsumleOLD.b |
. . . . 5
⊢ (𝜑 → (ℝ D (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐴)) = (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐵)) |
| 37 | 27, 34, 35, 36 | dvmptneg 25927 |
. . . 4
⊢ (𝜑 → (ℝ D (𝑥 ∈ (𝑀(,)𝑁) ↦ -𝐴)) = (𝑥 ∈ (𝑀(,)𝑁) ↦ -𝐵)) |
| 38 | | dvfsumleOLD.c |
. . . . 5
⊢ (𝑥 = 𝑀 → 𝐴 = 𝐶) |
| 39 | 38 | negeqd 11481 |
. . . 4
⊢ (𝑥 = 𝑀 → -𝐴 = -𝐶) |
| 40 | | dvfsumleOLD.d |
. . . . 5
⊢ (𝑥 = 𝑁 → 𝐴 = 𝐷) |
| 41 | 40 | negeqd 11481 |
. . . 4
⊢ (𝑥 = 𝑁 → -𝐴 = -𝐷) |
| 42 | | dvfsumleOLD.x |
. . . . 5
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → 𝑋 ∈ ℝ) |
| 43 | 42 | renegcld 11669 |
. . . 4
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → -𝑋 ∈ ℝ) |
| 44 | | dvfsumge.l |
. . . . 5
⊢ ((𝜑 ∧ (𝑘 ∈ (𝑀..^𝑁) ∧ 𝑥 ∈ (𝑘(,)(𝑘 + 1)))) → 𝐵 ≤ 𝑋) |
| 45 | 9 | adantr 480 |
. . . . . . . . . . . 12
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → 𝑀 ∈ ℝ) |
| 46 | 45 | rexrd 11290 |
. . . . . . . . . . 11
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → 𝑀 ∈
ℝ*) |
| 47 | | elfzole1 13689 |
. . . . . . . . . . . 12
⊢ (𝑘 ∈ (𝑀..^𝑁) → 𝑀 ≤ 𝑘) |
| 48 | 47 | adantl 481 |
. . . . . . . . . . 11
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → 𝑀 ≤ 𝑘) |
| 49 | | iooss1 13402 |
. . . . . . . . . . 11
⊢ ((𝑀 ∈ ℝ*
∧ 𝑀 ≤ 𝑘) → (𝑘(,)(𝑘 + 1)) ⊆ (𝑀(,)(𝑘 + 1))) |
| 50 | 46, 48, 49 | syl2anc 584 |
. . . . . . . . . 10
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → (𝑘(,)(𝑘 + 1)) ⊆ (𝑀(,)(𝑘 + 1))) |
| 51 | 12 | adantr 480 |
. . . . . . . . . . . 12
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → 𝑁 ∈ ℝ) |
| 52 | 51 | rexrd 11290 |
. . . . . . . . . . 11
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → 𝑁 ∈
ℝ*) |
| 53 | | fzofzp1 13785 |
. . . . . . . . . . . . 13
⊢ (𝑘 ∈ (𝑀..^𝑁) → (𝑘 + 1) ∈ (𝑀...𝑁)) |
| 54 | 53 | adantl 481 |
. . . . . . . . . . . 12
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → (𝑘 + 1) ∈ (𝑀...𝑁)) |
| 55 | | elfzle2 13550 |
. . . . . . . . . . . 12
⊢ ((𝑘 + 1) ∈ (𝑀...𝑁) → (𝑘 + 1) ≤ 𝑁) |
| 56 | 54, 55 | syl 17 |
. . . . . . . . . . 11
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → (𝑘 + 1) ≤ 𝑁) |
| 57 | | iooss2 13403 |
. . . . . . . . . . 11
⊢ ((𝑁 ∈ ℝ*
∧ (𝑘 + 1) ≤ 𝑁) → (𝑀(,)(𝑘 + 1)) ⊆ (𝑀(,)𝑁)) |
| 58 | 52, 56, 57 | syl2anc 584 |
. . . . . . . . . 10
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → (𝑀(,)(𝑘 + 1)) ⊆ (𝑀(,)𝑁)) |
| 59 | 50, 58 | sstrd 3974 |
. . . . . . . . 9
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → (𝑘(,)(𝑘 + 1)) ⊆ (𝑀(,)𝑁)) |
| 60 | 59 | sselda 3963 |
. . . . . . . 8
⊢ (((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) ∧ 𝑥 ∈ (𝑘(,)(𝑘 + 1))) → 𝑥 ∈ (𝑀(,)𝑁)) |
| 61 | 32 | adantlr 715 |
. . . . . . . . . . . . 13
⊢ (((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) ∧ 𝑥 ∈ (𝑀[,]𝑁)) → 𝐴 ∈ ℝ) |
| 62 | 29, 61 | sylan2 593 |
. . . . . . . . . . . 12
⊢ (((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) ∧ 𝑥 ∈ (𝑀(,)𝑁)) → 𝐴 ∈ ℝ) |
| 63 | 62 | fmpttd 7110 |
. . . . . . . . . . 11
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐴):(𝑀(,)𝑁)⟶ℝ) |
| 64 | | ioossre 13429 |
. . . . . . . . . . 11
⊢ (𝑀(,)𝑁) ⊆ ℝ |
| 65 | | dvfre 25912 |
. . . . . . . . . . 11
⊢ (((𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐴):(𝑀(,)𝑁)⟶ℝ ∧ (𝑀(,)𝑁) ⊆ ℝ) → (ℝ D (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐴)):dom (ℝ D (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐴))⟶ℝ) |
| 66 | 63, 64, 65 | sylancl 586 |
. . . . . . . . . 10
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → (ℝ D (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐴)):dom (ℝ D (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐴))⟶ℝ) |
| 67 | 36 | adantr 480 |
. . . . . . . . . . 11
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → (ℝ D (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐴)) = (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐵)) |
| 68 | 67 | dmeqd 5890 |
. . . . . . . . . . . 12
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → dom (ℝ D (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐴)) = dom (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐵)) |
| 69 | 35 | adantlr 715 |
. . . . . . . . . . . . . 14
⊢ (((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) ∧ 𝑥 ∈ (𝑀(,)𝑁)) → 𝐵 ∈ 𝑉) |
| 70 | 69 | ralrimiva 3133 |
. . . . . . . . . . . . 13
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → ∀𝑥 ∈ (𝑀(,)𝑁)𝐵 ∈ 𝑉) |
| 71 | | dmmptg 6236 |
. . . . . . . . . . . . 13
⊢
(∀𝑥 ∈
(𝑀(,)𝑁)𝐵 ∈ 𝑉 → dom (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐵) = (𝑀(,)𝑁)) |
| 72 | 70, 71 | syl 17 |
. . . . . . . . . . . 12
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → dom (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐵) = (𝑀(,)𝑁)) |
| 73 | 68, 72 | eqtrd 2771 |
. . . . . . . . . . 11
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → dom (ℝ D (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐴)) = (𝑀(,)𝑁)) |
| 74 | 67, 73 | feq12d 6699 |
. . . . . . . . . 10
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → ((ℝ D (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐴)):dom (ℝ D (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐴))⟶ℝ ↔ (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐵):(𝑀(,)𝑁)⟶ℝ)) |
| 75 | 66, 74 | mpbid 232 |
. . . . . . . . 9
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → (𝑥 ∈ (𝑀(,)𝑁) ↦ 𝐵):(𝑀(,)𝑁)⟶ℝ) |
| 76 | 75 | fvmptelcdm 7108 |
. . . . . . . 8
⊢ (((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) ∧ 𝑥 ∈ (𝑀(,)𝑁)) → 𝐵 ∈ ℝ) |
| 77 | 60, 76 | syldan 591 |
. . . . . . 7
⊢ (((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) ∧ 𝑥 ∈ (𝑘(,)(𝑘 + 1))) → 𝐵 ∈ ℝ) |
| 78 | 77 | anasss 466 |
. . . . . 6
⊢ ((𝜑 ∧ (𝑘 ∈ (𝑀..^𝑁) ∧ 𝑥 ∈ (𝑘(,)(𝑘 + 1)))) → 𝐵 ∈ ℝ) |
| 79 | 42 | adantrr 717 |
. . . . . 6
⊢ ((𝜑 ∧ (𝑘 ∈ (𝑀..^𝑁) ∧ 𝑥 ∈ (𝑘(,)(𝑘 + 1)))) → 𝑋 ∈ ℝ) |
| 80 | 78, 79 | lenegd 11821 |
. . . . 5
⊢ ((𝜑 ∧ (𝑘 ∈ (𝑀..^𝑁) ∧ 𝑥 ∈ (𝑘(,)(𝑘 + 1)))) → (𝐵 ≤ 𝑋 ↔ -𝑋 ≤ -𝐵)) |
| 81 | 44, 80 | mpbid 232 |
. . . 4
⊢ ((𝜑 ∧ (𝑘 ∈ (𝑀..^𝑁) ∧ 𝑥 ∈ (𝑘(,)(𝑘 + 1)))) → -𝑋 ≤ -𝐵) |
| 82 | 1, 23, 25, 37, 39, 41, 43, 81 | dvfsumle 25983 |
. . 3
⊢ (𝜑 → Σ𝑘 ∈ (𝑀..^𝑁)-𝑋 ≤ (-𝐷 − -𝐶)) |
| 83 | | fzofi 13997 |
. . . . 5
⊢ (𝑀..^𝑁) ∈ Fin |
| 84 | 83 | a1i 11 |
. . . 4
⊢ (𝜑 → (𝑀..^𝑁) ∈ Fin) |
| 85 | 42 | recnd 11268 |
. . . 4
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀..^𝑁)) → 𝑋 ∈ ℂ) |
| 86 | 84, 85 | fsumneg 15808 |
. . 3
⊢ (𝜑 → Σ𝑘 ∈ (𝑀..^𝑁)-𝑋 = -Σ𝑘 ∈ (𝑀..^𝑁)𝑋) |
| 87 | 40 | eleq1d 2820 |
. . . . . . 7
⊢ (𝑥 = 𝑁 → (𝐴 ∈ ℝ ↔ 𝐷 ∈ ℝ)) |
| 88 | | eqid 2736 |
. . . . . . . . 9
⊢ (𝑥 ∈ (𝑀[,]𝑁) ↦ 𝐴) = (𝑥 ∈ (𝑀[,]𝑁) ↦ 𝐴) |
| 89 | 88 | fmpt 7105 |
. . . . . . . 8
⊢
(∀𝑥 ∈
(𝑀[,]𝑁)𝐴 ∈ ℝ ↔ (𝑥 ∈ (𝑀[,]𝑁) ↦ 𝐴):(𝑀[,]𝑁)⟶ℝ) |
| 90 | 31, 89 | sylibr 234 |
. . . . . . 7
⊢ (𝜑 → ∀𝑥 ∈ (𝑀[,]𝑁)𝐴 ∈ ℝ) |
| 91 | 9 | rexrd 11290 |
. . . . . . . 8
⊢ (𝜑 → 𝑀 ∈
ℝ*) |
| 92 | 12 | rexrd 11290 |
. . . . . . . 8
⊢ (𝜑 → 𝑁 ∈
ℝ*) |
| 93 | | eluzle 12870 |
. . . . . . . . 9
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → 𝑀 ≤ 𝑁) |
| 94 | 1, 93 | syl 17 |
. . . . . . . 8
⊢ (𝜑 → 𝑀 ≤ 𝑁) |
| 95 | | ubicc2 13487 |
. . . . . . . 8
⊢ ((𝑀 ∈ ℝ*
∧ 𝑁 ∈
ℝ* ∧ 𝑀
≤ 𝑁) → 𝑁 ∈ (𝑀[,]𝑁)) |
| 96 | 91, 92, 94, 95 | syl3anc 1373 |
. . . . . . 7
⊢ (𝜑 → 𝑁 ∈ (𝑀[,]𝑁)) |
| 97 | 87, 90, 96 | rspcdva 3607 |
. . . . . 6
⊢ (𝜑 → 𝐷 ∈ ℝ) |
| 98 | 97 | recnd 11268 |
. . . . 5
⊢ (𝜑 → 𝐷 ∈ ℂ) |
| 99 | 38 | eleq1d 2820 |
. . . . . . 7
⊢ (𝑥 = 𝑀 → (𝐴 ∈ ℝ ↔ 𝐶 ∈ ℝ)) |
| 100 | | lbicc2 13486 |
. . . . . . . 8
⊢ ((𝑀 ∈ ℝ*
∧ 𝑁 ∈
ℝ* ∧ 𝑀
≤ 𝑁) → 𝑀 ∈ (𝑀[,]𝑁)) |
| 101 | 91, 92, 94, 100 | syl3anc 1373 |
. . . . . . 7
⊢ (𝜑 → 𝑀 ∈ (𝑀[,]𝑁)) |
| 102 | 99, 90, 101 | rspcdva 3607 |
. . . . . 6
⊢ (𝜑 → 𝐶 ∈ ℝ) |
| 103 | 102 | recnd 11268 |
. . . . 5
⊢ (𝜑 → 𝐶 ∈ ℂ) |
| 104 | 98, 103 | neg2subd 11616 |
. . . 4
⊢ (𝜑 → (-𝐷 − -𝐶) = (𝐶 − 𝐷)) |
| 105 | 98, 103 | negsubdi2d 11615 |
. . . 4
⊢ (𝜑 → -(𝐷 − 𝐶) = (𝐶 − 𝐷)) |
| 106 | 104, 105 | eqtr4d 2774 |
. . 3
⊢ (𝜑 → (-𝐷 − -𝐶) = -(𝐷 − 𝐶)) |
| 107 | 82, 86, 106 | 3brtr3d 5155 |
. 2
⊢ (𝜑 → -Σ𝑘 ∈ (𝑀..^𝑁)𝑋 ≤ -(𝐷 − 𝐶)) |
| 108 | 97, 102 | resubcld 11670 |
. . 3
⊢ (𝜑 → (𝐷 − 𝐶) ∈ ℝ) |
| 109 | 84, 42 | fsumrecl 15755 |
. . 3
⊢ (𝜑 → Σ𝑘 ∈ (𝑀..^𝑁)𝑋 ∈ ℝ) |
| 110 | 108, 109 | lenegd 11821 |
. 2
⊢ (𝜑 → ((𝐷 − 𝐶) ≤ Σ𝑘 ∈ (𝑀..^𝑁)𝑋 ↔ -Σ𝑘 ∈ (𝑀..^𝑁)𝑋 ≤ -(𝐷 − 𝐶))) |
| 111 | 107, 110 | mpbird 257 |
1
⊢ (𝜑 → (𝐷 − 𝐶) ≤ Σ𝑘 ∈ (𝑀..^𝑁)𝑋) |