| Step | Hyp | Ref
 | Expression | 
| 1 |   | isumss2.ss | 
. . . . 5
⊢ (𝜑 → 𝐴 ⊆ 𝐵) | 
| 2 | 1 | adantr 276 | 
. . . 4
⊢ ((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) → 𝐴 ⊆ 𝐵) | 
| 3 |   | isumss2.c | 
. . . . . 6
⊢ (𝜑 → ∀𝑘 ∈ 𝐴 𝐶 ∈ ℂ) | 
| 4 |   | iftrue 3566 | 
. . . . . . . 8
⊢ (𝑚 ∈ 𝐴 → if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) = ⦋𝑚 / 𝑘⦌𝐶) | 
| 5 | 4 | adantl 277 | 
. . . . . . 7
⊢
((∀𝑘 ∈
𝐴 𝐶 ∈ ℂ ∧ 𝑚 ∈ 𝐴) → if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) = ⦋𝑚 / 𝑘⦌𝐶) | 
| 6 |   | nfcsb1v 3117 | 
. . . . . . . . . 10
⊢
Ⅎ𝑘⦋𝑚 / 𝑘⦌𝐶 | 
| 7 | 6 | nfel1 2350 | 
. . . . . . . . 9
⊢
Ⅎ𝑘⦋𝑚 / 𝑘⦌𝐶 ∈ ℂ | 
| 8 |   | csbeq1a 3093 | 
. . . . . . . . . 10
⊢ (𝑘 = 𝑚 → 𝐶 = ⦋𝑚 / 𝑘⦌𝐶) | 
| 9 | 8 | eleq1d 2265 | 
. . . . . . . . 9
⊢ (𝑘 = 𝑚 → (𝐶 ∈ ℂ ↔ ⦋𝑚 / 𝑘⦌𝐶 ∈ ℂ)) | 
| 10 | 7, 9 | rspc 2862 | 
. . . . . . . 8
⊢ (𝑚 ∈ 𝐴 → (∀𝑘 ∈ 𝐴 𝐶 ∈ ℂ → ⦋𝑚 / 𝑘⦌𝐶 ∈ ℂ)) | 
| 11 | 10 | impcom 125 | 
. . . . . . 7
⊢
((∀𝑘 ∈
𝐴 𝐶 ∈ ℂ ∧ 𝑚 ∈ 𝐴) → ⦋𝑚 / 𝑘⦌𝐶 ∈ ℂ) | 
| 12 | 5, 11 | eqeltrd 2273 | 
. . . . . 6
⊢
((∀𝑘 ∈
𝐴 𝐶 ∈ ℂ ∧ 𝑚 ∈ 𝐴) → if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) ∈ ℂ) | 
| 13 | 3, 12 | sylan 283 | 
. . . . 5
⊢ ((𝜑 ∧ 𝑚 ∈ 𝐴) → if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) ∈ ℂ) | 
| 14 | 13 | adantlr 477 | 
. . . 4
⊢ (((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑚 ∈ 𝐴) → if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) ∈ ℂ) | 
| 15 |   | eldifn 3286 | 
. . . . . 6
⊢ (𝑚 ∈ (𝐵 ∖ 𝐴) → ¬ 𝑚 ∈ 𝐴) | 
| 16 | 15 | iffalsed 3571 | 
. . . . 5
⊢ (𝑚 ∈ (𝐵 ∖ 𝐴) → if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) = 0) | 
| 17 | 16 | adantl 277 | 
. . . 4
⊢ (((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑚 ∈ (𝐵 ∖ 𝐴)) → if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) = 0) | 
| 18 |   | isumss2.adc | 
. . . . . . . . . 10
⊢ (𝜑 → ∀𝑗 ∈ 𝐵 DECID 𝑗 ∈ 𝐴) | 
| 19 | 18 | adantr 276 | 
. . . . . . . . 9
⊢ ((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) → ∀𝑗 ∈ 𝐵 DECID 𝑗 ∈ 𝐴) | 
| 20 |   | eleq1w 2257 | 
. . . . . . . . . . 11
⊢ (𝑗 = 𝑎 → (𝑗 ∈ 𝐴 ↔ 𝑎 ∈ 𝐴)) | 
| 21 | 20 | dcbid 839 | 
. . . . . . . . . 10
⊢ (𝑗 = 𝑎 → (DECID 𝑗 ∈ 𝐴 ↔ DECID 𝑎 ∈ 𝐴)) | 
| 22 | 21 | cbvralv 2729 | 
. . . . . . . . 9
⊢
(∀𝑗 ∈
𝐵 DECID
𝑗 ∈ 𝐴 ↔ ∀𝑎 ∈ 𝐵 DECID 𝑎 ∈ 𝐴) | 
| 23 | 19, 22 | sylib 122 | 
. . . . . . . 8
⊢ ((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) → ∀𝑎 ∈ 𝐵 DECID 𝑎 ∈ 𝐴) | 
| 24 | 23 | r19.21bi 2585 | 
. . . . . . 7
⊢ (((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑎 ∈ 𝐵) → DECID 𝑎 ∈ 𝐴) | 
| 25 | 24 | adantlr 477 | 
. . . . . 6
⊢ ((((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑎 ∈ (ℤ≥‘𝑀)) ∧ 𝑎 ∈ 𝐵) → DECID 𝑎 ∈ 𝐴) | 
| 26 | 2 | adantr 276 | 
. . . . . . . . . 10
⊢ (((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑎 ∈ (ℤ≥‘𝑀)) → 𝐴 ⊆ 𝐵) | 
| 27 | 26 | ssneld 3185 | 
. . . . . . . . 9
⊢ (((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑎 ∈ (ℤ≥‘𝑀)) → (¬ 𝑎 ∈ 𝐵 → ¬ 𝑎 ∈ 𝐴)) | 
| 28 | 27 | imp 124 | 
. . . . . . . 8
⊢ ((((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑎 ∈ (ℤ≥‘𝑀)) ∧ ¬ 𝑎 ∈ 𝐵) → ¬ 𝑎 ∈ 𝐴) | 
| 29 | 28 | olcd 735 | 
. . . . . . 7
⊢ ((((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑎 ∈ (ℤ≥‘𝑀)) ∧ ¬ 𝑎 ∈ 𝐵) → (𝑎 ∈ 𝐴 ∨ ¬ 𝑎 ∈ 𝐴)) | 
| 30 |   | df-dc 836 | 
. . . . . . 7
⊢
(DECID 𝑎 ∈ 𝐴 ↔ (𝑎 ∈ 𝐴 ∨ ¬ 𝑎 ∈ 𝐴)) | 
| 31 | 29, 30 | sylibr 134 | 
. . . . . 6
⊢ ((((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑎 ∈ (ℤ≥‘𝑀)) ∧ ¬ 𝑎 ∈ 𝐵) → DECID 𝑎 ∈ 𝐴) | 
| 32 |   | eleq1w 2257 | 
. . . . . . . . 9
⊢ (𝑗 = 𝑎 → (𝑗 ∈ 𝐵 ↔ 𝑎 ∈ 𝐵)) | 
| 33 | 32 | dcbid 839 | 
. . . . . . . 8
⊢ (𝑗 = 𝑎 → (DECID 𝑗 ∈ 𝐵 ↔ DECID 𝑎 ∈ 𝐵)) | 
| 34 |   | simplr3 1043 | 
. . . . . . . 8
⊢ (((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑎 ∈ (ℤ≥‘𝑀)) → ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵) | 
| 35 |   | simpr 110 | 
. . . . . . . 8
⊢ (((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑎 ∈ (ℤ≥‘𝑀)) → 𝑎 ∈ (ℤ≥‘𝑀)) | 
| 36 | 33, 34, 35 | rspcdva 2873 | 
. . . . . . 7
⊢ (((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑎 ∈ (ℤ≥‘𝑀)) → DECID
𝑎 ∈ 𝐵) | 
| 37 |   | exmiddc 837 | 
. . . . . . 7
⊢
(DECID 𝑎 ∈ 𝐵 → (𝑎 ∈ 𝐵 ∨ ¬ 𝑎 ∈ 𝐵)) | 
| 38 | 36, 37 | syl 14 | 
. . . . . 6
⊢ (((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑎 ∈ (ℤ≥‘𝑀)) → (𝑎 ∈ 𝐵 ∨ ¬ 𝑎 ∈ 𝐵)) | 
| 39 | 25, 31, 38 | mpjaodan 799 | 
. . . . 5
⊢ (((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) ∧ 𝑎 ∈ (ℤ≥‘𝑀)) → DECID
𝑎 ∈ 𝐴) | 
| 40 | 39 | ralrimiva 2570 | 
. . . 4
⊢ ((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) → ∀𝑎 ∈ (ℤ≥‘𝑀)DECID 𝑎 ∈ 𝐴) | 
| 41 |   | simpr1 1005 | 
. . . 4
⊢ ((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) → 𝑀 ∈ ℤ) | 
| 42 |   | simpr2 1006 | 
. . . 4
⊢ ((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) → 𝐵 ⊆ (ℤ≥‘𝑀)) | 
| 43 |   | simpr3 1007 | 
. . . . 5
⊢ ((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) → ∀𝑗 ∈ (ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵) | 
| 44 | 33 | cbvralv 2729 | 
. . . . 5
⊢
(∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵 ↔ ∀𝑎 ∈ (ℤ≥‘𝑀)DECID 𝑎 ∈ 𝐵) | 
| 45 | 43, 44 | sylib 122 | 
. . . 4
⊢ ((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) → ∀𝑎 ∈ (ℤ≥‘𝑀)DECID 𝑎 ∈ 𝐵) | 
| 46 | 2, 14, 17, 40, 41, 42, 45 | isumss 11556 | 
. . 3
⊢ ((𝜑 ∧ (𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵)) → Σ𝑚 ∈ 𝐴 if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) = Σ𝑚 ∈ 𝐵 if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0)) | 
| 47 | 1 | adantr 276 | 
. . . 4
⊢ ((𝜑 ∧ 𝐵 ∈ Fin) → 𝐴 ⊆ 𝐵) | 
| 48 | 13 | adantlr 477 | 
. . . 4
⊢ (((𝜑 ∧ 𝐵 ∈ Fin) ∧ 𝑚 ∈ 𝐴) → if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) ∈ ℂ) | 
| 49 | 16 | adantl 277 | 
. . . 4
⊢ (((𝜑 ∧ 𝐵 ∈ Fin) ∧ 𝑚 ∈ (𝐵 ∖ 𝐴)) → if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) = 0) | 
| 50 | 18 | adantr 276 | 
. . . 4
⊢ ((𝜑 ∧ 𝐵 ∈ Fin) → ∀𝑗 ∈ 𝐵 DECID 𝑗 ∈ 𝐴) | 
| 51 |   | simpr 110 | 
. . . 4
⊢ ((𝜑 ∧ 𝐵 ∈ Fin) → 𝐵 ∈ Fin) | 
| 52 | 47, 48, 49, 50, 51 | fisumss 11557 | 
. . 3
⊢ ((𝜑 ∧ 𝐵 ∈ Fin) → Σ𝑚 ∈ 𝐴 if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) = Σ𝑚 ∈ 𝐵 if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0)) | 
| 53 |   | isumss2.b | 
. . 3
⊢ (𝜑 → ((𝑀 ∈ ℤ ∧ 𝐵 ⊆ (ℤ≥‘𝑀) ∧ ∀𝑗 ∈
(ℤ≥‘𝑀)DECID 𝑗 ∈ 𝐵) ∨ 𝐵 ∈ Fin)) | 
| 54 | 46, 52, 53 | mpjaodan 799 | 
. 2
⊢ (𝜑 → Σ𝑚 ∈ 𝐴 if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) = Σ𝑚 ∈ 𝐵 if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0)) | 
| 55 |   | iftrue 3566 | 
. . . 4
⊢ (𝑘 ∈ 𝐴 → if(𝑘 ∈ 𝐴, 𝐶, 0) = 𝐶) | 
| 56 | 55 | sumeq2i 11529 | 
. . 3
⊢
Σ𝑘 ∈
𝐴 if(𝑘 ∈ 𝐴, 𝐶, 0) = Σ𝑘 ∈ 𝐴 𝐶 | 
| 57 |   | nfcv 2339 | 
. . . 4
⊢
Ⅎ𝑚if(𝑘 ∈ 𝐴, 𝐶, 0) | 
| 58 |   | nfv 1542 | 
. . . . 5
⊢
Ⅎ𝑘 𝑚 ∈ 𝐴 | 
| 59 |   | nfcv 2339 | 
. . . . 5
⊢
Ⅎ𝑘0 | 
| 60 | 58, 6, 59 | nfif 3589 | 
. . . 4
⊢
Ⅎ𝑘if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) | 
| 61 |   | eleq1w 2257 | 
. . . . 5
⊢ (𝑘 = 𝑚 → (𝑘 ∈ 𝐴 ↔ 𝑚 ∈ 𝐴)) | 
| 62 | 61, 8 | ifbieq1d 3583 | 
. . . 4
⊢ (𝑘 = 𝑚 → if(𝑘 ∈ 𝐴, 𝐶, 0) = if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0)) | 
| 63 | 57, 60, 62 | cbvsumi 11527 | 
. . 3
⊢
Σ𝑘 ∈
𝐴 if(𝑘 ∈ 𝐴, 𝐶, 0) = Σ𝑚 ∈ 𝐴 if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) | 
| 64 | 56, 63 | eqtr3i 2219 | 
. 2
⊢
Σ𝑘 ∈
𝐴 𝐶 = Σ𝑚 ∈ 𝐴 if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) | 
| 65 | 57, 60, 62 | cbvsumi 11527 | 
. 2
⊢
Σ𝑘 ∈
𝐵 if(𝑘 ∈ 𝐴, 𝐶, 0) = Σ𝑚 ∈ 𝐵 if(𝑚 ∈ 𝐴, ⦋𝑚 / 𝑘⦌𝐶, 0) | 
| 66 | 54, 64, 65 | 3eqtr4g 2254 | 
1
⊢ (𝜑 → Σ𝑘 ∈ 𝐴 𝐶 = Σ𝑘 ∈ 𝐵 if(𝑘 ∈ 𝐴, 𝐶, 0)) |