Proof of Theorem telfsumo
Step | Hyp | Ref
| Expression |
1 | | sum0 11351 |
. . . 4
⊢
Σ𝑗 ∈
∅ (𝐵 − 𝐶) = 0 |
2 | | telfsumo.3 |
. . . . . . . 8
⊢ (𝑘 = 𝑀 → 𝐴 = 𝐷) |
3 | 2 | eleq1d 2239 |
. . . . . . 7
⊢ (𝑘 = 𝑀 → (𝐴 ∈ ℂ ↔ 𝐷 ∈ ℂ)) |
4 | | telfsumo.6 |
. . . . . . . 8
⊢ ((𝜑 ∧ 𝑘 ∈ (𝑀...𝑁)) → 𝐴 ∈ ℂ) |
5 | 4 | ralrimiva 2543 |
. . . . . . 7
⊢ (𝜑 → ∀𝑘 ∈ (𝑀...𝑁)𝐴 ∈ ℂ) |
6 | | telfsumo.5 |
. . . . . . . 8
⊢ (𝜑 → 𝑁 ∈ (ℤ≥‘𝑀)) |
7 | | eluzfz1 9987 |
. . . . . . . 8
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → 𝑀 ∈ (𝑀...𝑁)) |
8 | 6, 7 | syl 14 |
. . . . . . 7
⊢ (𝜑 → 𝑀 ∈ (𝑀...𝑁)) |
9 | 3, 5, 8 | rspcdva 2839 |
. . . . . 6
⊢ (𝜑 → 𝐷 ∈ ℂ) |
10 | 9 | adantr 274 |
. . . . 5
⊢ ((𝜑 ∧ 𝑁 = 𝑀) → 𝐷 ∈ ℂ) |
11 | 10 | subidd 8218 |
. . . 4
⊢ ((𝜑 ∧ 𝑁 = 𝑀) → (𝐷 − 𝐷) = 0) |
12 | 1, 11 | eqtr4id 2222 |
. . 3
⊢ ((𝜑 ∧ 𝑁 = 𝑀) → Σ𝑗 ∈ ∅ (𝐵 − 𝐶) = (𝐷 − 𝐷)) |
13 | | oveq2 5861 |
. . . . . 6
⊢ (𝑁 = 𝑀 → (𝑀..^𝑁) = (𝑀..^𝑀)) |
14 | 13 | adantl 275 |
. . . . 5
⊢ ((𝜑 ∧ 𝑁 = 𝑀) → (𝑀..^𝑁) = (𝑀..^𝑀)) |
15 | | fzo0 10124 |
. . . . 5
⊢ (𝑀..^𝑀) = ∅ |
16 | 14, 15 | eqtrdi 2219 |
. . . 4
⊢ ((𝜑 ∧ 𝑁 = 𝑀) → (𝑀..^𝑁) = ∅) |
17 | 16 | sumeq1d 11329 |
. . 3
⊢ ((𝜑 ∧ 𝑁 = 𝑀) → Σ𝑗 ∈ (𝑀..^𝑁)(𝐵 − 𝐶) = Σ𝑗 ∈ ∅ (𝐵 − 𝐶)) |
18 | | eqeq1 2177 |
. . . . . . . 8
⊢ (𝑘 = 𝑁 → (𝑘 = 𝑀 ↔ 𝑁 = 𝑀)) |
19 | | telfsumo.4 |
. . . . . . . . 9
⊢ (𝑘 = 𝑁 → 𝐴 = 𝐸) |
20 | 19 | eqeq1d 2179 |
. . . . . . . 8
⊢ (𝑘 = 𝑁 → (𝐴 = 𝐷 ↔ 𝐸 = 𝐷)) |
21 | 18, 20 | imbi12d 233 |
. . . . . . 7
⊢ (𝑘 = 𝑁 → ((𝑘 = 𝑀 → 𝐴 = 𝐷) ↔ (𝑁 = 𝑀 → 𝐸 = 𝐷))) |
22 | 21, 2 | vtoclg 2790 |
. . . . . 6
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → (𝑁 = 𝑀 → 𝐸 = 𝐷)) |
23 | 22 | imp 123 |
. . . . 5
⊢ ((𝑁 ∈
(ℤ≥‘𝑀) ∧ 𝑁 = 𝑀) → 𝐸 = 𝐷) |
24 | 6, 23 | sylan 281 |
. . . 4
⊢ ((𝜑 ∧ 𝑁 = 𝑀) → 𝐸 = 𝐷) |
25 | 24 | oveq2d 5869 |
. . 3
⊢ ((𝜑 ∧ 𝑁 = 𝑀) → (𝐷 − 𝐸) = (𝐷 − 𝐷)) |
26 | 12, 17, 25 | 3eqtr4d 2213 |
. 2
⊢ ((𝜑 ∧ 𝑁 = 𝑀) → Σ𝑗 ∈ (𝑀..^𝑁)(𝐵 − 𝐶) = (𝐷 − 𝐸)) |
27 | | eluzel2 9492 |
. . . . . . 7
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → 𝑀 ∈ ℤ) |
28 | 6, 27 | syl 14 |
. . . . . 6
⊢ (𝜑 → 𝑀 ∈ ℤ) |
29 | | eluzelz 9496 |
. . . . . . 7
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → 𝑁 ∈ ℤ) |
30 | 6, 29 | syl 14 |
. . . . . 6
⊢ (𝜑 → 𝑁 ∈ ℤ) |
31 | | fzofig 10388 |
. . . . . 6
⊢ ((𝑀 ∈ ℤ ∧ 𝑁 ∈ ℤ) → (𝑀..^𝑁) ∈ Fin) |
32 | 28, 30, 31 | syl2anc 409 |
. . . . 5
⊢ (𝜑 → (𝑀..^𝑁) ∈ Fin) |
33 | | telfsumo.1 |
. . . . . . 7
⊢ (𝑘 = 𝑗 → 𝐴 = 𝐵) |
34 | 33 | eleq1d 2239 |
. . . . . 6
⊢ (𝑘 = 𝑗 → (𝐴 ∈ ℂ ↔ 𝐵 ∈ ℂ)) |
35 | 5 | adantr 274 |
. . . . . 6
⊢ ((𝜑 ∧ 𝑗 ∈ (𝑀..^𝑁)) → ∀𝑘 ∈ (𝑀...𝑁)𝐴 ∈ ℂ) |
36 | | elfzofz 10118 |
. . . . . . 7
⊢ (𝑗 ∈ (𝑀..^𝑁) → 𝑗 ∈ (𝑀...𝑁)) |
37 | 36 | adantl 275 |
. . . . . 6
⊢ ((𝜑 ∧ 𝑗 ∈ (𝑀..^𝑁)) → 𝑗 ∈ (𝑀...𝑁)) |
38 | 34, 35, 37 | rspcdva 2839 |
. . . . 5
⊢ ((𝜑 ∧ 𝑗 ∈ (𝑀..^𝑁)) → 𝐵 ∈ ℂ) |
39 | | telfsumo.2 |
. . . . . . 7
⊢ (𝑘 = (𝑗 + 1) → 𝐴 = 𝐶) |
40 | 39 | eleq1d 2239 |
. . . . . 6
⊢ (𝑘 = (𝑗 + 1) → (𝐴 ∈ ℂ ↔ 𝐶 ∈ ℂ)) |
41 | | fzofzp1 10183 |
. . . . . . 7
⊢ (𝑗 ∈ (𝑀..^𝑁) → (𝑗 + 1) ∈ (𝑀...𝑁)) |
42 | 41 | adantl 275 |
. . . . . 6
⊢ ((𝜑 ∧ 𝑗 ∈ (𝑀..^𝑁)) → (𝑗 + 1) ∈ (𝑀...𝑁)) |
43 | 40, 35, 42 | rspcdva 2839 |
. . . . 5
⊢ ((𝜑 ∧ 𝑗 ∈ (𝑀..^𝑁)) → 𝐶 ∈ ℂ) |
44 | 32, 38, 43 | fsumsub 11415 |
. . . 4
⊢ (𝜑 → Σ𝑗 ∈ (𝑀..^𝑁)(𝐵 − 𝐶) = (Σ𝑗 ∈ (𝑀..^𝑁)𝐵 − Σ𝑗 ∈ (𝑀..^𝑁)𝐶)) |
45 | 44 | adantr 274 |
. . 3
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → Σ𝑗 ∈ (𝑀..^𝑁)(𝐵 − 𝐶) = (Σ𝑗 ∈ (𝑀..^𝑁)𝐵 − Σ𝑗 ∈ (𝑀..^𝑁)𝐶)) |
46 | 33 | cbvsumv 11324 |
. . . . 5
⊢
Σ𝑘 ∈
(𝑀..^𝑁)𝐴 = Σ𝑗 ∈ (𝑀..^𝑁)𝐵 |
47 | | eluzp1m1 9510 |
. . . . . . . 8
⊢ ((𝑀 ∈ ℤ ∧ 𝑁 ∈
(ℤ≥‘(𝑀 + 1))) → (𝑁 − 1) ∈
(ℤ≥‘𝑀)) |
48 | 28, 47 | sylan 281 |
. . . . . . 7
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → (𝑁 − 1) ∈
(ℤ≥‘𝑀)) |
49 | 30 | adantr 274 |
. . . . . . . . . . 11
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → 𝑁 ∈ ℤ) |
50 | | fzoval 10104 |
. . . . . . . . . . 11
⊢ (𝑁 ∈ ℤ → (𝑀..^𝑁) = (𝑀...(𝑁 − 1))) |
51 | 49, 50 | syl 14 |
. . . . . . . . . 10
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → (𝑀..^𝑁) = (𝑀...(𝑁 − 1))) |
52 | | fzossfz 10121 |
. . . . . . . . . 10
⊢ (𝑀..^𝑁) ⊆ (𝑀...𝑁) |
53 | 51, 52 | eqsstrrdi 3200 |
. . . . . . . . 9
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → (𝑀...(𝑁 − 1)) ⊆ (𝑀...𝑁)) |
54 | 53 | sselda 3147 |
. . . . . . . 8
⊢ (((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) ∧ 𝑘 ∈ (𝑀...(𝑁 − 1))) → 𝑘 ∈ (𝑀...𝑁)) |
55 | 4 | adantlr 474 |
. . . . . . . 8
⊢ (((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) ∧ 𝑘 ∈ (𝑀...𝑁)) → 𝐴 ∈ ℂ) |
56 | 54, 55 | syldan 280 |
. . . . . . 7
⊢ (((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) ∧ 𝑘 ∈ (𝑀...(𝑁 − 1))) → 𝐴 ∈ ℂ) |
57 | 48, 56, 2 | fsum1p 11381 |
. . . . . 6
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → Σ𝑘 ∈ (𝑀...(𝑁 − 1))𝐴 = (𝐷 + Σ𝑘 ∈ ((𝑀 + 1)...(𝑁 − 1))𝐴)) |
58 | 51 | sumeq1d 11329 |
. . . . . 6
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → Σ𝑘 ∈ (𝑀..^𝑁)𝐴 = Σ𝑘 ∈ (𝑀...(𝑁 − 1))𝐴) |
59 | | fzoval 10104 |
. . . . . . . . 9
⊢ (𝑁 ∈ ℤ → ((𝑀 + 1)..^𝑁) = ((𝑀 + 1)...(𝑁 − 1))) |
60 | 49, 59 | syl 14 |
. . . . . . . 8
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → ((𝑀 + 1)..^𝑁) = ((𝑀 + 1)...(𝑁 − 1))) |
61 | 60 | sumeq1d 11329 |
. . . . . . 7
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴 = Σ𝑘 ∈ ((𝑀 + 1)...(𝑁 − 1))𝐴) |
62 | 61 | oveq2d 5869 |
. . . . . 6
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → (𝐷 + Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴) = (𝐷 + Σ𝑘 ∈ ((𝑀 + 1)...(𝑁 − 1))𝐴)) |
63 | 57, 58, 62 | 3eqtr4d 2213 |
. . . . 5
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → Σ𝑘 ∈ (𝑀..^𝑁)𝐴 = (𝐷 + Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴)) |
64 | 46, 63 | eqtr3id 2217 |
. . . 4
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → Σ𝑗 ∈ (𝑀..^𝑁)𝐵 = (𝐷 + Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴)) |
65 | | simpr 109 |
. . . . . 6
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) |
66 | | fzp1ss 10029 |
. . . . . . . . . 10
⊢ (𝑀 ∈ ℤ → ((𝑀 + 1)...𝑁) ⊆ (𝑀...𝑁)) |
67 | 28, 66 | syl 14 |
. . . . . . . . 9
⊢ (𝜑 → ((𝑀 + 1)...𝑁) ⊆ (𝑀...𝑁)) |
68 | 67 | sselda 3147 |
. . . . . . . 8
⊢ ((𝜑 ∧ 𝑘 ∈ ((𝑀 + 1)...𝑁)) → 𝑘 ∈ (𝑀...𝑁)) |
69 | 68, 4 | syldan 280 |
. . . . . . 7
⊢ ((𝜑 ∧ 𝑘 ∈ ((𝑀 + 1)...𝑁)) → 𝐴 ∈ ℂ) |
70 | 69 | adantlr 474 |
. . . . . 6
⊢ (((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) ∧ 𝑘 ∈ ((𝑀 + 1)...𝑁)) → 𝐴 ∈ ℂ) |
71 | 65, 70, 19 | fsumm1 11379 |
. . . . 5
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → Σ𝑘 ∈ ((𝑀 + 1)...𝑁)𝐴 = (Σ𝑘 ∈ ((𝑀 + 1)...(𝑁 − 1))𝐴 + 𝐸)) |
72 | | 1zzd 9239 |
. . . . . . . 8
⊢ (𝜑 → 1 ∈
ℤ) |
73 | 28 | peano2zd 9337 |
. . . . . . . 8
⊢ (𝜑 → (𝑀 + 1) ∈ ℤ) |
74 | 72, 73, 30, 69, 39 | fsumshftm 11408 |
. . . . . . 7
⊢ (𝜑 → Σ𝑘 ∈ ((𝑀 + 1)...𝑁)𝐴 = Σ𝑗 ∈ (((𝑀 + 1) − 1)...(𝑁 − 1))𝐶) |
75 | 28 | zcnd 9335 |
. . . . . . . . . . 11
⊢ (𝜑 → 𝑀 ∈ ℂ) |
76 | | ax-1cn 7867 |
. . . . . . . . . . 11
⊢ 1 ∈
ℂ |
77 | | pncan 8125 |
. . . . . . . . . . 11
⊢ ((𝑀 ∈ ℂ ∧ 1 ∈
ℂ) → ((𝑀 + 1)
− 1) = 𝑀) |
78 | 75, 76, 77 | sylancl 411 |
. . . . . . . . . 10
⊢ (𝜑 → ((𝑀 + 1) − 1) = 𝑀) |
79 | 78 | oveq1d 5868 |
. . . . . . . . 9
⊢ (𝜑 → (((𝑀 + 1) − 1)...(𝑁 − 1)) = (𝑀...(𝑁 − 1))) |
80 | 30, 50 | syl 14 |
. . . . . . . . 9
⊢ (𝜑 → (𝑀..^𝑁) = (𝑀...(𝑁 − 1))) |
81 | 79, 80 | eqtr4d 2206 |
. . . . . . . 8
⊢ (𝜑 → (((𝑀 + 1) − 1)...(𝑁 − 1)) = (𝑀..^𝑁)) |
82 | 81 | sumeq1d 11329 |
. . . . . . 7
⊢ (𝜑 → Σ𝑗 ∈ (((𝑀 + 1) − 1)...(𝑁 − 1))𝐶 = Σ𝑗 ∈ (𝑀..^𝑁)𝐶) |
83 | 74, 82 | eqtrd 2203 |
. . . . . 6
⊢ (𝜑 → Σ𝑘 ∈ ((𝑀 + 1)...𝑁)𝐴 = Σ𝑗 ∈ (𝑀..^𝑁)𝐶) |
84 | 83 | adantr 274 |
. . . . 5
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → Σ𝑘 ∈ ((𝑀 + 1)...𝑁)𝐴 = Σ𝑗 ∈ (𝑀..^𝑁)𝐶) |
85 | 30, 59 | syl 14 |
. . . . . . . . 9
⊢ (𝜑 → ((𝑀 + 1)..^𝑁) = ((𝑀 + 1)...(𝑁 − 1))) |
86 | 85 | sumeq1d 11329 |
. . . . . . . 8
⊢ (𝜑 → Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴 = Σ𝑘 ∈ ((𝑀 + 1)...(𝑁 − 1))𝐴) |
87 | 86 | oveq1d 5868 |
. . . . . . 7
⊢ (𝜑 → (Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴 + 𝐸) = (Σ𝑘 ∈ ((𝑀 + 1)...(𝑁 − 1))𝐴 + 𝐸)) |
88 | | fzofig 10388 |
. . . . . . . . . 10
⊢ (((𝑀 + 1) ∈ ℤ ∧ 𝑁 ∈ ℤ) → ((𝑀 + 1)..^𝑁) ∈ Fin) |
89 | 73, 30, 88 | syl2anc 409 |
. . . . . . . . 9
⊢ (𝜑 → ((𝑀 + 1)..^𝑁) ∈ Fin) |
90 | | elfzofz 10118 |
. . . . . . . . . 10
⊢ (𝑘 ∈ ((𝑀 + 1)..^𝑁) → 𝑘 ∈ ((𝑀 + 1)...𝑁)) |
91 | 90, 69 | sylan2 284 |
. . . . . . . . 9
⊢ ((𝜑 ∧ 𝑘 ∈ ((𝑀 + 1)..^𝑁)) → 𝐴 ∈ ℂ) |
92 | 89, 91 | fsumcl 11363 |
. . . . . . . 8
⊢ (𝜑 → Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴 ∈ ℂ) |
93 | 19 | eleq1d 2239 |
. . . . . . . . 9
⊢ (𝑘 = 𝑁 → (𝐴 ∈ ℂ ↔ 𝐸 ∈ ℂ)) |
94 | | eluzfz2 9988 |
. . . . . . . . . 10
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → 𝑁 ∈ (𝑀...𝑁)) |
95 | 6, 94 | syl 14 |
. . . . . . . . 9
⊢ (𝜑 → 𝑁 ∈ (𝑀...𝑁)) |
96 | 93, 5, 95 | rspcdva 2839 |
. . . . . . . 8
⊢ (𝜑 → 𝐸 ∈ ℂ) |
97 | 92, 96 | addcomd 8070 |
. . . . . . 7
⊢ (𝜑 → (Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴 + 𝐸) = (𝐸 + Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴)) |
98 | 87, 97 | eqtr3d 2205 |
. . . . . 6
⊢ (𝜑 → (Σ𝑘 ∈ ((𝑀 + 1)...(𝑁 − 1))𝐴 + 𝐸) = (𝐸 + Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴)) |
99 | 98 | adantr 274 |
. . . . 5
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → (Σ𝑘 ∈ ((𝑀 + 1)...(𝑁 − 1))𝐴 + 𝐸) = (𝐸 + Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴)) |
100 | 71, 84, 99 | 3eqtr3d 2211 |
. . . 4
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → Σ𝑗 ∈ (𝑀..^𝑁)𝐶 = (𝐸 + Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴)) |
101 | 64, 100 | oveq12d 5871 |
. . 3
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → (Σ𝑗 ∈ (𝑀..^𝑁)𝐵 − Σ𝑗 ∈ (𝑀..^𝑁)𝐶) = ((𝐷 + Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴) − (𝐸 + Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴))) |
102 | 9, 96, 92 | pnpcan2d 8268 |
. . . 4
⊢ (𝜑 → ((𝐷 + Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴) − (𝐸 + Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴)) = (𝐷 − 𝐸)) |
103 | 102 | adantr 274 |
. . 3
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → ((𝐷 + Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴) − (𝐸 + Σ𝑘 ∈ ((𝑀 + 1)..^𝑁)𝐴)) = (𝐷 − 𝐸)) |
104 | 45, 101, 103 | 3eqtrd 2207 |
. 2
⊢ ((𝜑 ∧ 𝑁 ∈ (ℤ≥‘(𝑀 + 1))) → Σ𝑗 ∈ (𝑀..^𝑁)(𝐵 − 𝐶) = (𝐷 − 𝐸)) |
105 | | uzp1 9520 |
. . 3
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → (𝑁 = 𝑀 ∨ 𝑁 ∈ (ℤ≥‘(𝑀 + 1)))) |
106 | 6, 105 | syl 14 |
. 2
⊢ (𝜑 → (𝑁 = 𝑀 ∨ 𝑁 ∈ (ℤ≥‘(𝑀 + 1)))) |
107 | 26, 104, 106 | mpjaodan 793 |
1
⊢ (𝜑 → Σ𝑗 ∈ (𝑀..^𝑁)(𝐵 − 𝐶) = (𝐷 − 𝐸)) |