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Mirrors > Home > ILE Home > Th. List > nn0ge2m1nn | GIF version |
Description: If a nonnegative integer is greater than or equal to two, the integer decreased by 1 is a positive integer. (Contributed by Alexander van der Vekens, 1-Aug-2018.) (Revised by AV, 4-Jan-2020.) |
Ref | Expression |
---|---|
nn0ge2m1nn | ⊢ ((𝑁 ∈ ℕ0 ∧ 2 ≤ 𝑁) → (𝑁 − 1) ∈ ℕ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | simpl 108 | . . . . 5 ⊢ ((𝑁 ∈ ℕ0 ∧ 2 ≤ 𝑁) → 𝑁 ∈ ℕ0) | |
2 | 1red 7774 | . . . . . . . 8 ⊢ (𝑁 ∈ ℕ0 → 1 ∈ ℝ) | |
3 | 2re 8783 | . . . . . . . . 9 ⊢ 2 ∈ ℝ | |
4 | 3 | a1i 9 | . . . . . . . 8 ⊢ (𝑁 ∈ ℕ0 → 2 ∈ ℝ) |
5 | nn0re 8979 | . . . . . . . 8 ⊢ (𝑁 ∈ ℕ0 → 𝑁 ∈ ℝ) | |
6 | 2, 4, 5 | 3jca 1161 | . . . . . . 7 ⊢ (𝑁 ∈ ℕ0 → (1 ∈ ℝ ∧ 2 ∈ ℝ ∧ 𝑁 ∈ ℝ)) |
7 | 6 | adantr 274 | . . . . . 6 ⊢ ((𝑁 ∈ ℕ0 ∧ 2 ≤ 𝑁) → (1 ∈ ℝ ∧ 2 ∈ ℝ ∧ 𝑁 ∈ ℝ)) |
8 | simpr 109 | . . . . . . 7 ⊢ ((𝑁 ∈ ℕ0 ∧ 2 ≤ 𝑁) → 2 ≤ 𝑁) | |
9 | 1lt2 8882 | . . . . . . 7 ⊢ 1 < 2 | |
10 | 8, 9 | jctil 310 | . . . . . 6 ⊢ ((𝑁 ∈ ℕ0 ∧ 2 ≤ 𝑁) → (1 < 2 ∧ 2 ≤ 𝑁)) |
11 | ltleletr 7839 | . . . . . 6 ⊢ ((1 ∈ ℝ ∧ 2 ∈ ℝ ∧ 𝑁 ∈ ℝ) → ((1 < 2 ∧ 2 ≤ 𝑁) → 1 ≤ 𝑁)) | |
12 | 7, 10, 11 | sylc 62 | . . . . 5 ⊢ ((𝑁 ∈ ℕ0 ∧ 2 ≤ 𝑁) → 1 ≤ 𝑁) |
13 | elnnnn0c 9015 | . . . . 5 ⊢ (𝑁 ∈ ℕ ↔ (𝑁 ∈ ℕ0 ∧ 1 ≤ 𝑁)) | |
14 | 1, 12, 13 | sylanbrc 413 | . . . 4 ⊢ ((𝑁 ∈ ℕ0 ∧ 2 ≤ 𝑁) → 𝑁 ∈ ℕ) |
15 | nn1m1nn 8731 | . . . 4 ⊢ (𝑁 ∈ ℕ → (𝑁 = 1 ∨ (𝑁 − 1) ∈ ℕ)) | |
16 | 14, 15 | syl 14 | . . 3 ⊢ ((𝑁 ∈ ℕ0 ∧ 2 ≤ 𝑁) → (𝑁 = 1 ∨ (𝑁 − 1) ∈ ℕ)) |
17 | 1re 7758 | . . . . . . . . . . 11 ⊢ 1 ∈ ℝ | |
18 | 3, 17 | lenlti 7857 | . . . . . . . . . 10 ⊢ (2 ≤ 1 ↔ ¬ 1 < 2) |
19 | 18 | biimpi 119 | . . . . . . . . 9 ⊢ (2 ≤ 1 → ¬ 1 < 2) |
20 | 9, 19 | mt2 629 | . . . . . . . 8 ⊢ ¬ 2 ≤ 1 |
21 | breq2 3928 | . . . . . . . 8 ⊢ (𝑁 = 1 → (2 ≤ 𝑁 ↔ 2 ≤ 1)) | |
22 | 20, 21 | mtbiri 664 | . . . . . . 7 ⊢ (𝑁 = 1 → ¬ 2 ≤ 𝑁) |
23 | 22 | pm2.21d 608 | . . . . . 6 ⊢ (𝑁 = 1 → (2 ≤ 𝑁 → (𝑁 − 1) ∈ ℕ)) |
24 | 23 | com12 30 | . . . . 5 ⊢ (2 ≤ 𝑁 → (𝑁 = 1 → (𝑁 − 1) ∈ ℕ)) |
25 | 24 | adantl 275 | . . . 4 ⊢ ((𝑁 ∈ ℕ0 ∧ 2 ≤ 𝑁) → (𝑁 = 1 → (𝑁 − 1) ∈ ℕ)) |
26 | 25 | orim1d 776 | . . 3 ⊢ ((𝑁 ∈ ℕ0 ∧ 2 ≤ 𝑁) → ((𝑁 = 1 ∨ (𝑁 − 1) ∈ ℕ) → ((𝑁 − 1) ∈ ℕ ∨ (𝑁 − 1) ∈ ℕ))) |
27 | 16, 26 | mpd 13 | . 2 ⊢ ((𝑁 ∈ ℕ0 ∧ 2 ≤ 𝑁) → ((𝑁 − 1) ∈ ℕ ∨ (𝑁 − 1) ∈ ℕ)) |
28 | oridm 746 | . 2 ⊢ (((𝑁 − 1) ∈ ℕ ∨ (𝑁 − 1) ∈ ℕ) ↔ (𝑁 − 1) ∈ ℕ) | |
29 | 27, 28 | sylib 121 | 1 ⊢ ((𝑁 ∈ ℕ0 ∧ 2 ≤ 𝑁) → (𝑁 − 1) ∈ ℕ) |
Colors of variables: wff set class |
Syntax hints: ¬ wn 3 → wi 4 ∧ wa 103 ∨ wo 697 ∧ w3a 962 = wceq 1331 ∈ wcel 1480 class class class wbr 3924 (class class class)co 5767 ℝcr 7612 1c1 7614 < clt 7793 ≤ cle 7794 − cmin 7926 ℕcn 8713 2c2 8764 ℕ0cn0 8970 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-ia1 105 ax-ia2 106 ax-ia3 107 ax-in1 603 ax-in2 604 ax-io 698 ax-5 1423 ax-7 1424 ax-gen 1425 ax-ie1 1469 ax-ie2 1470 ax-8 1482 ax-10 1483 ax-11 1484 ax-i12 1485 ax-bndl 1486 ax-4 1487 ax-13 1491 ax-14 1492 ax-17 1506 ax-i9 1510 ax-ial 1514 ax-i5r 1515 ax-ext 2119 ax-sep 4041 ax-pow 4093 ax-pr 4126 ax-un 4350 ax-setind 4447 ax-cnex 7704 ax-resscn 7705 ax-1cn 7706 ax-1re 7707 ax-icn 7708 ax-addcl 7709 ax-addrcl 7710 ax-mulcl 7711 ax-addcom 7713 ax-addass 7715 ax-distr 7717 ax-i2m1 7718 ax-0lt1 7719 ax-0id 7721 ax-rnegex 7722 ax-cnre 7724 ax-pre-ltirr 7725 ax-pre-ltwlin 7726 ax-pre-lttrn 7727 ax-pre-ltadd 7729 |
This theorem depends on definitions: df-bi 116 df-3an 964 df-tru 1334 df-fal 1337 df-nf 1437 df-sb 1736 df-eu 2000 df-mo 2001 df-clab 2124 df-cleq 2130 df-clel 2133 df-nfc 2268 df-ne 2307 df-nel 2402 df-ral 2419 df-rex 2420 df-reu 2421 df-rab 2423 df-v 2683 df-sbc 2905 df-dif 3068 df-un 3070 df-in 3072 df-ss 3079 df-pw 3507 df-sn 3528 df-pr 3529 df-op 3531 df-uni 3732 df-int 3767 df-br 3925 df-opab 3985 df-id 4210 df-xp 4540 df-rel 4541 df-cnv 4542 df-co 4543 df-dm 4544 df-iota 5083 df-fun 5120 df-fv 5126 df-riota 5723 df-ov 5770 df-oprab 5771 df-mpo 5772 df-pnf 7795 df-mnf 7796 df-xr 7797 df-ltxr 7798 df-le 7799 df-sub 7928 df-inn 8714 df-2 8772 df-n0 8971 |
This theorem is referenced by: nn0ge2m1nn0 9031 |
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