| Step | Hyp | Ref
 | Expression | 
| 1 |   | df-sumdc 11519 | 
. 2
⊢
Σ𝑘 ∈
𝐴 𝐵 = (℩𝑧(∃𝑚 ∈ ℤ (𝐴 ⊆ (ℤ≥‘𝑚) ∧ ∀𝑗 ∈
(ℤ≥‘𝑚)DECID 𝑗 ∈ 𝐴 ∧ seq𝑚( + , (𝑛 ∈ ℤ ↦ if(𝑛 ∈ 𝐴, ⦋𝑛 / 𝑘⦌𝐵, 0))) ⇝ 𝑧) ∨ ∃𝑚 ∈ ℕ ∃𝑓(𝑓:(1...𝑚)–1-1-onto→𝐴 ∧ 𝑧 = (seq1( + , (𝑛 ∈ ℕ ↦ if(𝑛 ≤ 𝑚, ⦋(𝑓‘𝑛) / 𝑘⦌𝐵, 0)))‘𝑚)))) | 
| 2 |   | nfcv 2339 | 
. . . . 5
⊢
Ⅎ𝑥ℤ | 
| 3 |   | nfsum.1 | 
. . . . . . 7
⊢
Ⅎ𝑥𝐴 | 
| 4 |   | nfcv 2339 | 
. . . . . . 7
⊢
Ⅎ𝑥(ℤ≥‘𝑚) | 
| 5 | 3, 4 | nfss 3176 | 
. . . . . 6
⊢
Ⅎ𝑥 𝐴 ⊆
(ℤ≥‘𝑚) | 
| 6 | 3 | nfcri 2333 | 
. . . . . . . 8
⊢
Ⅎ𝑥 𝑗 ∈ 𝐴 | 
| 7 | 6 | nfdc 1673 | 
. . . . . . 7
⊢
Ⅎ𝑥DECID 𝑗 ∈ 𝐴 | 
| 8 | 4, 7 | nfralxy 2535 | 
. . . . . 6
⊢
Ⅎ𝑥∀𝑗 ∈ (ℤ≥‘𝑚)DECID 𝑗 ∈ 𝐴 | 
| 9 |   | nfcv 2339 | 
. . . . . . . 8
⊢
Ⅎ𝑥𝑚 | 
| 10 |   | nfcv 2339 | 
. . . . . . . 8
⊢
Ⅎ𝑥
+ | 
| 11 | 3 | nfcri 2333 | 
. . . . . . . . . 10
⊢
Ⅎ𝑥 𝑛 ∈ 𝐴 | 
| 12 |   | nfcv 2339 | 
. . . . . . . . . . 11
⊢
Ⅎ𝑥𝑛 | 
| 13 |   | nfsum.2 | 
. . . . . . . . . . 11
⊢
Ⅎ𝑥𝐵 | 
| 14 | 12, 13 | nfcsb 3122 | 
. . . . . . . . . 10
⊢
Ⅎ𝑥⦋𝑛 / 𝑘⦌𝐵 | 
| 15 |   | nfcv 2339 | 
. . . . . . . . . 10
⊢
Ⅎ𝑥0 | 
| 16 | 11, 14, 15 | nfif 3589 | 
. . . . . . . . 9
⊢
Ⅎ𝑥if(𝑛 ∈ 𝐴, ⦋𝑛 / 𝑘⦌𝐵, 0) | 
| 17 | 2, 16 | nfmpt 4125 | 
. . . . . . . 8
⊢
Ⅎ𝑥(𝑛 ∈ ℤ ↦ if(𝑛 ∈ 𝐴, ⦋𝑛 / 𝑘⦌𝐵, 0)) | 
| 18 | 9, 10, 17 | nfseq 10549 | 
. . . . . . 7
⊢
Ⅎ𝑥seq𝑚( + , (𝑛 ∈ ℤ ↦ if(𝑛 ∈ 𝐴, ⦋𝑛 / 𝑘⦌𝐵, 0))) | 
| 19 |   | nfcv 2339 | 
. . . . . . 7
⊢
Ⅎ𝑥
⇝ | 
| 20 |   | nfcv 2339 | 
. . . . . . 7
⊢
Ⅎ𝑥𝑧 | 
| 21 | 18, 19, 20 | nfbr 4079 | 
. . . . . 6
⊢
Ⅎ𝑥seq𝑚( + , (𝑛 ∈ ℤ ↦ if(𝑛 ∈ 𝐴, ⦋𝑛 / 𝑘⦌𝐵, 0))) ⇝ 𝑧 | 
| 22 | 5, 8, 21 | nf3an 1580 | 
. . . . 5
⊢
Ⅎ𝑥(𝐴 ⊆
(ℤ≥‘𝑚) ∧ ∀𝑗 ∈ (ℤ≥‘𝑚)DECID 𝑗 ∈ 𝐴 ∧ seq𝑚( + , (𝑛 ∈ ℤ ↦ if(𝑛 ∈ 𝐴, ⦋𝑛 / 𝑘⦌𝐵, 0))) ⇝ 𝑧) | 
| 23 | 2, 22 | nfrexw 2536 | 
. . . 4
⊢
Ⅎ𝑥∃𝑚 ∈ ℤ (𝐴 ⊆
(ℤ≥‘𝑚) ∧ ∀𝑗 ∈ (ℤ≥‘𝑚)DECID 𝑗 ∈ 𝐴 ∧ seq𝑚( + , (𝑛 ∈ ℤ ↦ if(𝑛 ∈ 𝐴, ⦋𝑛 / 𝑘⦌𝐵, 0))) ⇝ 𝑧) | 
| 24 |   | nfcv 2339 | 
. . . . 5
⊢
Ⅎ𝑥ℕ | 
| 25 |   | nfcv 2339 | 
. . . . . . . 8
⊢
Ⅎ𝑥𝑓 | 
| 26 |   | nfcv 2339 | 
. . . . . . . 8
⊢
Ⅎ𝑥(1...𝑚) | 
| 27 | 25, 26, 3 | nff1o 5502 | 
. . . . . . 7
⊢
Ⅎ𝑥 𝑓:(1...𝑚)–1-1-onto→𝐴 | 
| 28 |   | nfcv 2339 | 
. . . . . . . . . 10
⊢
Ⅎ𝑥1 | 
| 29 |   | nfv 1542 | 
. . . . . . . . . . . 12
⊢
Ⅎ𝑥 𝑛 ≤ 𝑚 | 
| 30 |   | nfcv 2339 | 
. . . . . . . . . . . . 13
⊢
Ⅎ𝑥(𝑓‘𝑛) | 
| 31 | 30, 13 | nfcsb 3122 | 
. . . . . . . . . . . 12
⊢
Ⅎ𝑥⦋(𝑓‘𝑛) / 𝑘⦌𝐵 | 
| 32 | 29, 31, 15 | nfif 3589 | 
. . . . . . . . . . 11
⊢
Ⅎ𝑥if(𝑛 ≤ 𝑚, ⦋(𝑓‘𝑛) / 𝑘⦌𝐵, 0) | 
| 33 | 24, 32 | nfmpt 4125 | 
. . . . . . . . . 10
⊢
Ⅎ𝑥(𝑛 ∈ ℕ ↦ if(𝑛 ≤ 𝑚, ⦋(𝑓‘𝑛) / 𝑘⦌𝐵, 0)) | 
| 34 | 28, 10, 33 | nfseq 10549 | 
. . . . . . . . 9
⊢
Ⅎ𝑥seq1(
+ , (𝑛 ∈ ℕ
↦ if(𝑛 ≤ 𝑚, ⦋(𝑓‘𝑛) / 𝑘⦌𝐵, 0))) | 
| 35 | 34, 9 | nffv 5568 | 
. . . . . . . 8
⊢
Ⅎ𝑥(seq1( + , (𝑛 ∈ ℕ ↦ if(𝑛 ≤ 𝑚, ⦋(𝑓‘𝑛) / 𝑘⦌𝐵, 0)))‘𝑚) | 
| 36 | 35 | nfeq2 2351 | 
. . . . . . 7
⊢
Ⅎ𝑥 𝑧 = (seq1( + , (𝑛 ∈ ℕ ↦ if(𝑛 ≤ 𝑚, ⦋(𝑓‘𝑛) / 𝑘⦌𝐵, 0)))‘𝑚) | 
| 37 | 27, 36 | nfan 1579 | 
. . . . . 6
⊢
Ⅎ𝑥(𝑓:(1...𝑚)–1-1-onto→𝐴 ∧ 𝑧 = (seq1( + , (𝑛 ∈ ℕ ↦ if(𝑛 ≤ 𝑚, ⦋(𝑓‘𝑛) / 𝑘⦌𝐵, 0)))‘𝑚)) | 
| 38 | 37 | nfex 1651 | 
. . . . 5
⊢
Ⅎ𝑥∃𝑓(𝑓:(1...𝑚)–1-1-onto→𝐴 ∧ 𝑧 = (seq1( + , (𝑛 ∈ ℕ ↦ if(𝑛 ≤ 𝑚, ⦋(𝑓‘𝑛) / 𝑘⦌𝐵, 0)))‘𝑚)) | 
| 39 | 24, 38 | nfrexw 2536 | 
. . . 4
⊢
Ⅎ𝑥∃𝑚 ∈ ℕ ∃𝑓(𝑓:(1...𝑚)–1-1-onto→𝐴 ∧ 𝑧 = (seq1( + , (𝑛 ∈ ℕ ↦ if(𝑛 ≤ 𝑚, ⦋(𝑓‘𝑛) / 𝑘⦌𝐵, 0)))‘𝑚)) | 
| 40 | 23, 39 | nfor 1588 | 
. . 3
⊢
Ⅎ𝑥(∃𝑚 ∈ ℤ (𝐴 ⊆ (ℤ≥‘𝑚) ∧ ∀𝑗 ∈
(ℤ≥‘𝑚)DECID 𝑗 ∈ 𝐴 ∧ seq𝑚( + , (𝑛 ∈ ℤ ↦ if(𝑛 ∈ 𝐴, ⦋𝑛 / 𝑘⦌𝐵, 0))) ⇝ 𝑧) ∨ ∃𝑚 ∈ ℕ ∃𝑓(𝑓:(1...𝑚)–1-1-onto→𝐴 ∧ 𝑧 = (seq1( + , (𝑛 ∈ ℕ ↦ if(𝑛 ≤ 𝑚, ⦋(𝑓‘𝑛) / 𝑘⦌𝐵, 0)))‘𝑚))) | 
| 41 | 40 | nfiotaw 5223 | 
. 2
⊢
Ⅎ𝑥(℩𝑧(∃𝑚 ∈ ℤ (𝐴 ⊆ (ℤ≥‘𝑚) ∧ ∀𝑗 ∈
(ℤ≥‘𝑚)DECID 𝑗 ∈ 𝐴 ∧ seq𝑚( + , (𝑛 ∈ ℤ ↦ if(𝑛 ∈ 𝐴, ⦋𝑛 / 𝑘⦌𝐵, 0))) ⇝ 𝑧) ∨ ∃𝑚 ∈ ℕ ∃𝑓(𝑓:(1...𝑚)–1-1-onto→𝐴 ∧ 𝑧 = (seq1( + , (𝑛 ∈ ℕ ↦ if(𝑛 ≤ 𝑚, ⦋(𝑓‘𝑛) / 𝑘⦌𝐵, 0)))‘𝑚)))) | 
| 42 | 1, 41 | nfcxfr 2336 | 
1
⊢
Ⅎ𝑥Σ𝑘 ∈ 𝐴 𝐵 |