Proof of Theorem fznatpl1
| Step | Hyp | Ref
 | Expression | 
| 1 |   | 1red 8041 | 
. . 3
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → 1 ∈
ℝ) | 
| 2 |   | elfzelz 10100 | 
. . . . . 6
⊢ (𝐼 ∈ (1...(𝑁 − 1)) → 𝐼 ∈ ℤ) | 
| 3 | 2 | zred 9448 | 
. . . . 5
⊢ (𝐼 ∈ (1...(𝑁 − 1)) → 𝐼 ∈ ℝ) | 
| 4 | 3 | adantl 277 | 
. . . 4
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → 𝐼 ∈ ℝ) | 
| 5 |   | peano2re 8162 | 
. . . 4
⊢ (𝐼 ∈ ℝ → (𝐼 + 1) ∈
ℝ) | 
| 6 | 4, 5 | syl 14 | 
. . 3
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → (𝐼 + 1) ∈ ℝ) | 
| 7 |   | peano2re 8162 | 
. . . . 5
⊢ (1 ∈
ℝ → (1 + 1) ∈ ℝ) | 
| 8 | 1, 7 | syl 14 | 
. . . 4
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → (1 + 1) ∈
ℝ) | 
| 9 | 1 | ltp1d 8957 | 
. . . 4
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → 1 < (1 +
1)) | 
| 10 |   | elfzle1 10102 | 
. . . . . 6
⊢ (𝐼 ∈ (1...(𝑁 − 1)) → 1 ≤ 𝐼) | 
| 11 | 10 | adantl 277 | 
. . . . 5
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → 1 ≤ 𝐼) | 
| 12 |   | 1re 8025 | 
. . . . . . 7
⊢ 1 ∈
ℝ | 
| 13 |   | leadd1 8457 | 
. . . . . . 7
⊢ ((1
∈ ℝ ∧ 𝐼
∈ ℝ ∧ 1 ∈ ℝ) → (1 ≤ 𝐼 ↔ (1 + 1) ≤ (𝐼 + 1))) | 
| 14 | 12, 12, 13 | mp3an13 1339 | 
. . . . . 6
⊢ (𝐼 ∈ ℝ → (1 ≤
𝐼 ↔ (1 + 1) ≤
(𝐼 + 1))) | 
| 15 | 4, 14 | syl 14 | 
. . . . 5
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → (1 ≤ 𝐼 ↔ (1 + 1) ≤ (𝐼 + 1))) | 
| 16 | 11, 15 | mpbid 147 | 
. . . 4
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → (1 + 1) ≤ (𝐼 + 1)) | 
| 17 | 1, 8, 6, 9, 16 | ltletrd 8450 | 
. . 3
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → 1 < (𝐼 + 1)) | 
| 18 | 1, 6, 17 | ltled 8145 | 
. 2
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → 1 ≤ (𝐼 + 1)) | 
| 19 |   | elfzle2 10103 | 
. . . 4
⊢ (𝐼 ∈ (1...(𝑁 − 1)) → 𝐼 ≤ (𝑁 − 1)) | 
| 20 | 19 | adantl 277 | 
. . 3
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → 𝐼 ≤ (𝑁 − 1)) | 
| 21 |   | nnz 9345 | 
. . . . . 6
⊢ (𝑁 ∈ ℕ → 𝑁 ∈
ℤ) | 
| 22 | 21 | adantr 276 | 
. . . . 5
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → 𝑁 ∈ ℤ) | 
| 23 | 22 | zred 9448 | 
. . . 4
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → 𝑁 ∈ ℝ) | 
| 24 |   | leaddsub 8465 | 
. . . . 5
⊢ ((𝐼 ∈ ℝ ∧ 1 ∈
ℝ ∧ 𝑁 ∈
ℝ) → ((𝐼 + 1)
≤ 𝑁 ↔ 𝐼 ≤ (𝑁 − 1))) | 
| 25 | 12, 24 | mp3an2 1336 | 
. . . 4
⊢ ((𝐼 ∈ ℝ ∧ 𝑁 ∈ ℝ) → ((𝐼 + 1) ≤ 𝑁 ↔ 𝐼 ≤ (𝑁 − 1))) | 
| 26 | 4, 23, 25 | syl2anc 411 | 
. . 3
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → ((𝐼 + 1) ≤ 𝑁 ↔ 𝐼 ≤ (𝑁 − 1))) | 
| 27 | 20, 26 | mpbird 167 | 
. 2
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → (𝐼 + 1) ≤ 𝑁) | 
| 28 | 2 | peano2zd 9451 | 
. . . 4
⊢ (𝐼 ∈ (1...(𝑁 − 1)) → (𝐼 + 1) ∈ ℤ) | 
| 29 | 28 | adantl 277 | 
. . 3
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → (𝐼 + 1) ∈ ℤ) | 
| 30 |   | 1z 9352 | 
. . . 4
⊢ 1 ∈
ℤ | 
| 31 |   | elfz 10089 | 
. . . 4
⊢ (((𝐼 + 1) ∈ ℤ ∧ 1
∈ ℤ ∧ 𝑁
∈ ℤ) → ((𝐼
+ 1) ∈ (1...𝑁) ↔
(1 ≤ (𝐼 + 1) ∧
(𝐼 + 1) ≤ 𝑁))) | 
| 32 | 30, 31 | mp3an2 1336 | 
. . 3
⊢ (((𝐼 + 1) ∈ ℤ ∧ 𝑁 ∈ ℤ) → ((𝐼 + 1) ∈ (1...𝑁) ↔ (1 ≤ (𝐼 + 1) ∧ (𝐼 + 1) ≤ 𝑁))) | 
| 33 | 29, 22, 32 | syl2anc 411 | 
. 2
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → ((𝐼 + 1) ∈ (1...𝑁) ↔ (1 ≤ (𝐼 + 1) ∧ (𝐼 + 1) ≤ 𝑁))) | 
| 34 | 18, 27, 33 | mpbir2and 946 | 
1
⊢ ((𝑁 ∈ ℕ ∧ 𝐼 ∈ (1...(𝑁 − 1))) → (𝐼 + 1) ∈ (1...𝑁)) |