| Step | Hyp | Ref
 | Expression | 
| 1 |   | eluzelz 9610 | 
. . . . . . . 8
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → 𝑁 ∈ ℤ) | 
| 2 |   | eluzelz 9610 | 
. . . . . . . 8
⊢ (𝑘 ∈
(ℤ≥‘𝑀) → 𝑘 ∈ ℤ) | 
| 3 |   | zlelttric 9371 | 
. . . . . . . 8
⊢ ((𝑁 ∈ ℤ ∧ 𝑘 ∈ ℤ) → (𝑁 ≤ 𝑘 ∨ 𝑘 < 𝑁)) | 
| 4 | 1, 2, 3 | syl2an 289 | 
. . . . . . 7
⊢ ((𝑁 ∈
(ℤ≥‘𝑀) ∧ 𝑘 ∈ (ℤ≥‘𝑀)) → (𝑁 ≤ 𝑘 ∨ 𝑘 < 𝑁)) | 
| 5 |   | eluz 9614 | 
. . . . . . . . 9
⊢ ((𝑁 ∈ ℤ ∧ 𝑘 ∈ ℤ) → (𝑘 ∈
(ℤ≥‘𝑁) ↔ 𝑁 ≤ 𝑘)) | 
| 6 | 1, 2, 5 | syl2an 289 | 
. . . . . . . 8
⊢ ((𝑁 ∈
(ℤ≥‘𝑀) ∧ 𝑘 ∈ (ℤ≥‘𝑀)) → (𝑘 ∈ (ℤ≥‘𝑁) ↔ 𝑁 ≤ 𝑘)) | 
| 7 |   | eluzel2 9606 | 
. . . . . . . . . 10
⊢ (𝑘 ∈
(ℤ≥‘𝑀) → 𝑀 ∈ ℤ) | 
| 8 |   | elfzm11 10166 | 
. . . . . . . . . . 11
⊢ ((𝑀 ∈ ℤ ∧ 𝑁 ∈ ℤ) → (𝑘 ∈ (𝑀...(𝑁 − 1)) ↔ (𝑘 ∈ ℤ ∧ 𝑀 ≤ 𝑘 ∧ 𝑘 < 𝑁))) | 
| 9 |   | df-3an 982 | 
. . . . . . . . . . 11
⊢ ((𝑘 ∈ ℤ ∧ 𝑀 ≤ 𝑘 ∧ 𝑘 < 𝑁) ↔ ((𝑘 ∈ ℤ ∧ 𝑀 ≤ 𝑘) ∧ 𝑘 < 𝑁)) | 
| 10 | 8, 9 | bitrdi 196 | 
. . . . . . . . . 10
⊢ ((𝑀 ∈ ℤ ∧ 𝑁 ∈ ℤ) → (𝑘 ∈ (𝑀...(𝑁 − 1)) ↔ ((𝑘 ∈ ℤ ∧ 𝑀 ≤ 𝑘) ∧ 𝑘 < 𝑁))) | 
| 11 | 7, 1, 10 | syl2anr 290 | 
. . . . . . . . 9
⊢ ((𝑁 ∈
(ℤ≥‘𝑀) ∧ 𝑘 ∈ (ℤ≥‘𝑀)) → (𝑘 ∈ (𝑀...(𝑁 − 1)) ↔ ((𝑘 ∈ ℤ ∧ 𝑀 ≤ 𝑘) ∧ 𝑘 < 𝑁))) | 
| 12 |   | eluzle 9613 | 
. . . . . . . . . . . 12
⊢ (𝑘 ∈
(ℤ≥‘𝑀) → 𝑀 ≤ 𝑘) | 
| 13 | 2, 12 | jca 306 | 
. . . . . . . . . . 11
⊢ (𝑘 ∈
(ℤ≥‘𝑀) → (𝑘 ∈ ℤ ∧ 𝑀 ≤ 𝑘)) | 
| 14 | 13 | adantl 277 | 
. . . . . . . . . 10
⊢ ((𝑁 ∈
(ℤ≥‘𝑀) ∧ 𝑘 ∈ (ℤ≥‘𝑀)) → (𝑘 ∈ ℤ ∧ 𝑀 ≤ 𝑘)) | 
| 15 | 14 | biantrurd 305 | 
. . . . . . . . 9
⊢ ((𝑁 ∈
(ℤ≥‘𝑀) ∧ 𝑘 ∈ (ℤ≥‘𝑀)) → (𝑘 < 𝑁 ↔ ((𝑘 ∈ ℤ ∧ 𝑀 ≤ 𝑘) ∧ 𝑘 < 𝑁))) | 
| 16 | 11, 15 | bitr4d 191 | 
. . . . . . . 8
⊢ ((𝑁 ∈
(ℤ≥‘𝑀) ∧ 𝑘 ∈ (ℤ≥‘𝑀)) → (𝑘 ∈ (𝑀...(𝑁 − 1)) ↔ 𝑘 < 𝑁)) | 
| 17 | 6, 16 | orbi12d 794 | 
. . . . . . 7
⊢ ((𝑁 ∈
(ℤ≥‘𝑀) ∧ 𝑘 ∈ (ℤ≥‘𝑀)) → ((𝑘 ∈ (ℤ≥‘𝑁) ∨ 𝑘 ∈ (𝑀...(𝑁 − 1))) ↔ (𝑁 ≤ 𝑘 ∨ 𝑘 < 𝑁))) | 
| 18 | 4, 17 | mpbird 167 | 
. . . . . 6
⊢ ((𝑁 ∈
(ℤ≥‘𝑀) ∧ 𝑘 ∈ (ℤ≥‘𝑀)) → (𝑘 ∈ (ℤ≥‘𝑁) ∨ 𝑘 ∈ (𝑀...(𝑁 − 1)))) | 
| 19 | 18 | orcomd 730 | 
. . . . 5
⊢ ((𝑁 ∈
(ℤ≥‘𝑀) ∧ 𝑘 ∈ (ℤ≥‘𝑀)) → (𝑘 ∈ (𝑀...(𝑁 − 1)) ∨ 𝑘 ∈ (ℤ≥‘𝑁))) | 
| 20 | 19 | ex 115 | 
. . . 4
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → (𝑘 ∈ (ℤ≥‘𝑀) → (𝑘 ∈ (𝑀...(𝑁 − 1)) ∨ 𝑘 ∈ (ℤ≥‘𝑁)))) | 
| 21 |   | elfzuz 10096 | 
. . . . . 6
⊢ (𝑘 ∈ (𝑀...(𝑁 − 1)) → 𝑘 ∈ (ℤ≥‘𝑀)) | 
| 22 | 21 | a1i 9 | 
. . . . 5
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → (𝑘 ∈ (𝑀...(𝑁 − 1)) → 𝑘 ∈ (ℤ≥‘𝑀))) | 
| 23 |   | uztrn 9618 | 
. . . . . 6
⊢ ((𝑘 ∈
(ℤ≥‘𝑁) ∧ 𝑁 ∈ (ℤ≥‘𝑀)) → 𝑘 ∈ (ℤ≥‘𝑀)) | 
| 24 | 23 | expcom 116 | 
. . . . 5
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → (𝑘 ∈ (ℤ≥‘𝑁) → 𝑘 ∈ (ℤ≥‘𝑀))) | 
| 25 | 22, 24 | jaod 718 | 
. . . 4
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → ((𝑘 ∈ (𝑀...(𝑁 − 1)) ∨ 𝑘 ∈ (ℤ≥‘𝑁)) → 𝑘 ∈ (ℤ≥‘𝑀))) | 
| 26 | 20, 25 | impbid 129 | 
. . 3
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → (𝑘 ∈ (ℤ≥‘𝑀) ↔ (𝑘 ∈ (𝑀...(𝑁 − 1)) ∨ 𝑘 ∈ (ℤ≥‘𝑁)))) | 
| 27 |   | elun 3304 | 
. . 3
⊢ (𝑘 ∈ ((𝑀...(𝑁 − 1)) ∪
(ℤ≥‘𝑁)) ↔ (𝑘 ∈ (𝑀...(𝑁 − 1)) ∨ 𝑘 ∈ (ℤ≥‘𝑁))) | 
| 28 | 26, 27 | bitr4di 198 | 
. 2
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → (𝑘 ∈ (ℤ≥‘𝑀) ↔ 𝑘 ∈ ((𝑀...(𝑁 − 1)) ∪
(ℤ≥‘𝑁)))) | 
| 29 | 28 | eqrdv 2194 | 
1
⊢ (𝑁 ∈
(ℤ≥‘𝑀) → (ℤ≥‘𝑀) = ((𝑀...(𝑁 − 1)) ∪
(ℤ≥‘𝑁))) |