Proof of Theorem ssfz12
| Step | Hyp | Ref
 | Expression | 
| 1 |   | eluz 12873 | 
. . . 4
⊢ ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ) → (𝐿 ∈
(ℤ≥‘𝐾) ↔ 𝐾 ≤ 𝐿)) | 
| 2 | 1 | biimp3ar 1471 | 
. . 3
⊢ ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → 𝐿 ∈ (ℤ≥‘𝐾)) | 
| 3 |   | eluzfz1 13552 | 
. . 3
⊢ (𝐿 ∈
(ℤ≥‘𝐾) → 𝐾 ∈ (𝐾...𝐿)) | 
| 4 | 2, 3 | syl 17 | 
. 2
⊢ ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → 𝐾 ∈ (𝐾...𝐿)) | 
| 5 |   | eluzfz2 13553 | 
. . . 4
⊢ (𝐿 ∈
(ℤ≥‘𝐾) → 𝐿 ∈ (𝐾...𝐿)) | 
| 6 | 2, 5 | syl 17 | 
. . 3
⊢ ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → 𝐿 ∈ (𝐾...𝐿)) | 
| 7 |   | ssel2 3958 | 
. . . . . . . 8
⊢ (((𝐾...𝐿) ⊆ (𝑀...𝑁) ∧ 𝐾 ∈ (𝐾...𝐿)) → 𝐾 ∈ (𝑀...𝑁)) | 
| 8 |   | ssel2 3958 | 
. . . . . . . . . . 11
⊢ (((𝐾...𝐿) ⊆ (𝑀...𝑁) ∧ 𝐿 ∈ (𝐾...𝐿)) → 𝐿 ∈ (𝑀...𝑁)) | 
| 9 |   | elfzuz3 13542 | 
. . . . . . . . . . 11
⊢ (𝐿 ∈ (𝑀...𝑁) → 𝑁 ∈ (ℤ≥‘𝐿)) | 
| 10 |   | eluz2 12865 | 
. . . . . . . . . . . . 13
⊢ (𝐾 ∈
(ℤ≥‘𝑀) ↔ (𝑀 ∈ ℤ ∧ 𝐾 ∈ ℤ ∧ 𝑀 ≤ 𝐾)) | 
| 11 |   | eluz2 12865 | 
. . . . . . . . . . . . . . . . 17
⊢ (𝑁 ∈
(ℤ≥‘𝐿) ↔ (𝐿 ∈ ℤ ∧ 𝑁 ∈ ℤ ∧ 𝐿 ≤ 𝑁)) | 
| 12 |   | pm3.21 471 | 
. . . . . . . . . . . . . . . . . 18
⊢ (𝐿 ≤ 𝑁 → (𝑀 ≤ 𝐾 → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁))) | 
| 13 | 12 | 3ad2ant3 1135 | 
. . . . . . . . . . . . . . . . 17
⊢ ((𝐿 ∈ ℤ ∧ 𝑁 ∈ ℤ ∧ 𝐿 ≤ 𝑁) → (𝑀 ≤ 𝐾 → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁))) | 
| 14 | 11, 13 | sylbi 217 | 
. . . . . . . . . . . . . . . 16
⊢ (𝑁 ∈
(ℤ≥‘𝐿) → (𝑀 ≤ 𝐾 → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁))) | 
| 15 | 14 | a1i 11 | 
. . . . . . . . . . . . . . 15
⊢ ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → (𝑁 ∈ (ℤ≥‘𝐿) → (𝑀 ≤ 𝐾 → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁)))) | 
| 16 | 15 | com13 88 | 
. . . . . . . . . . . . . 14
⊢ (𝑀 ≤ 𝐾 → (𝑁 ∈ (ℤ≥‘𝐿) → ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁)))) | 
| 17 | 16 | 3ad2ant3 1135 | 
. . . . . . . . . . . . 13
⊢ ((𝑀 ∈ ℤ ∧ 𝐾 ∈ ℤ ∧ 𝑀 ≤ 𝐾) → (𝑁 ∈ (ℤ≥‘𝐿) → ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁)))) | 
| 18 | 10, 17 | sylbi 217 | 
. . . . . . . . . . . 12
⊢ (𝐾 ∈
(ℤ≥‘𝑀) → (𝑁 ∈ (ℤ≥‘𝐿) → ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁)))) | 
| 19 |   | elfzuz 13541 | 
. . . . . . . . . . . 12
⊢ (𝐾 ∈ (𝑀...𝑁) → 𝐾 ∈ (ℤ≥‘𝑀)) | 
| 20 | 18, 19 | syl11 33 | 
. . . . . . . . . . 11
⊢ (𝑁 ∈
(ℤ≥‘𝐿) → (𝐾 ∈ (𝑀...𝑁) → ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁)))) | 
| 21 | 8, 9, 20 | 3syl 18 | 
. . . . . . . . . 10
⊢ (((𝐾...𝐿) ⊆ (𝑀...𝑁) ∧ 𝐿 ∈ (𝐾...𝐿)) → (𝐾 ∈ (𝑀...𝑁) → ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁)))) | 
| 22 | 21 | ex 412 | 
. . . . . . . . 9
⊢ ((𝐾...𝐿) ⊆ (𝑀...𝑁) → (𝐿 ∈ (𝐾...𝐿) → (𝐾 ∈ (𝑀...𝑁) → ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁))))) | 
| 23 | 22 | com4t 93 | 
. . . . . . . 8
⊢ (𝐾 ∈ (𝑀...𝑁) → ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → ((𝐾...𝐿) ⊆ (𝑀...𝑁) → (𝐿 ∈ (𝐾...𝐿) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁))))) | 
| 24 | 7, 23 | syl 17 | 
. . . . . . 7
⊢ (((𝐾...𝐿) ⊆ (𝑀...𝑁) ∧ 𝐾 ∈ (𝐾...𝐿)) → ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → ((𝐾...𝐿) ⊆ (𝑀...𝑁) → (𝐿 ∈ (𝐾...𝐿) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁))))) | 
| 25 | 24 | ex 412 | 
. . . . . 6
⊢ ((𝐾...𝐿) ⊆ (𝑀...𝑁) → (𝐾 ∈ (𝐾...𝐿) → ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → ((𝐾...𝐿) ⊆ (𝑀...𝑁) → (𝐿 ∈ (𝐾...𝐿) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁)))))) | 
| 26 | 25 | com24 95 | 
. . . . 5
⊢ ((𝐾...𝐿) ⊆ (𝑀...𝑁) → ((𝐾...𝐿) ⊆ (𝑀...𝑁) → ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → (𝐾 ∈ (𝐾...𝐿) → (𝐿 ∈ (𝐾...𝐿) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁)))))) | 
| 27 | 26 | pm2.43i 52 | 
. . . 4
⊢ ((𝐾...𝐿) ⊆ (𝑀...𝑁) → ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → (𝐾 ∈ (𝐾...𝐿) → (𝐿 ∈ (𝐾...𝐿) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁))))) | 
| 28 | 27 | com14 96 | 
. . 3
⊢ (𝐿 ∈ (𝐾...𝐿) → ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → (𝐾 ∈ (𝐾...𝐿) → ((𝐾...𝐿) ⊆ (𝑀...𝑁) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁))))) | 
| 29 | 6, 28 | mpcom 38 | 
. 2
⊢ ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → (𝐾 ∈ (𝐾...𝐿) → ((𝐾...𝐿) ⊆ (𝑀...𝑁) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁)))) | 
| 30 | 4, 29 | mpd 15 | 
1
⊢ ((𝐾 ∈ ℤ ∧ 𝐿 ∈ ℤ ∧ 𝐾 ≤ 𝐿) → ((𝐾...𝐿) ⊆ (𝑀...𝑁) → (𝑀 ≤ 𝐾 ∧ 𝐿 ≤ 𝑁))) |