nno - Metamath Proof Explorer

	Metamath Proof Explorer		< Previous Next > Nearby theorems
Mirrors > Home > MPE Home > Th. List > nno		Structured version Visualization version GIF version

Theorem nno 16321

Description: An alternate characterization of an odd integer greater than 1. (Contributed by AV, 2-Jun-2020.) (Proof shortened by AV, 10-Jul-2022.)

**Assertion**
Ref	Expression
nno	⊢ ((𝑁 ∈ (ℤ_≥‘2) ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) → ((𝑁 − 1) / 2) ∈ ℕ)

**Proof of Theorem nno**
Step	Hyp	Ref	Expression
1		eluz2b3 12902	. . 3 ⊢ (𝑁 ∈ (ℤ_≥‘2) ↔ (𝑁 ∈ ℕ ∧ 𝑁 ≠ 1))
2		nnnn0 12475	. . . . . 6 ⊢ (𝑁 ∈ ℕ → 𝑁 ∈ ℕ₀)
3		nn0o1gt2 16320	. . . . . 6 ⊢ ((𝑁 ∈ ℕ₀ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) → (𝑁 = 1 ∨ 2 < 𝑁))
4	2, 3	sylan 580	. . . . 5 ⊢ ((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) → (𝑁 = 1 ∨ 2 < 𝑁))
5		eqneqall 2951	. . . . . . 7 ⊢ (𝑁 = 1 → (𝑁 ≠ 1 → ((𝑁 − 1) / 2) ∈ ℕ))
6	5	a1d 25	. . . . . 6 ⊢ (𝑁 = 1 → ((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) → (𝑁 ≠ 1 → ((𝑁 − 1) / 2) ∈ ℕ)))
7		nn0z 12579	. . . . . . . . . . . 12 ⊢ (((𝑁 + 1) / 2) ∈ ℕ₀ → ((𝑁 + 1) / 2) ∈ ℤ)
8		peano2zm 12601	. . . . . . . . . . . 12 ⊢ (((𝑁 + 1) / 2) ∈ ℤ → (((𝑁 + 1) / 2) − 1) ∈ ℤ)
9	7, 8	syl 17	. . . . . . . . . . 11 ⊢ (((𝑁 + 1) / 2) ∈ ℕ₀ → (((𝑁 + 1) / 2) − 1) ∈ ℤ)
10	9	ad2antlr 725	. . . . . . . . . 10 ⊢ (((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) ∧ 2 < 𝑁) → (((𝑁 + 1) / 2) − 1) ∈ ℤ)
11		2cn 12283	. . . . . . . . . . . . . . 15 ⊢ 2 ∈ ℂ
12	11	mullidi 11215	. . . . . . . . . . . . . 14 ⊢ (1 · 2) = 2
13		nnre 12215	. . . . . . . . . . . . . . . . 17 ⊢ (𝑁 ∈ ℕ → 𝑁 ∈ ℝ)
14	13	ltp1d 12140	. . . . . . . . . . . . . . . 16 ⊢ (𝑁 ∈ ℕ → 𝑁 < (𝑁 + 1))
15	14	adantr 481	. . . . . . . . . . . . . . 15 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → 𝑁 < (𝑁 + 1))
16		2re 12282	. . . . . . . . . . . . . . . . 17 ⊢ 2 ∈ ℝ
17		peano2nn 12220	. . . . . . . . . . . . . . . . . 18 ⊢ (𝑁 ∈ ℕ → (𝑁 + 1) ∈ ℕ)
18	17	nnred 12223	. . . . . . . . . . . . . . . . 17 ⊢ (𝑁 ∈ ℕ → (𝑁 + 1) ∈ ℝ)
19		lttr 11286	. . . . . . . . . . . . . . . . 17 ⊢ ((2 ∈ ℝ ∧ 𝑁 ∈ ℝ ∧ (𝑁 + 1) ∈ ℝ) → ((2 < 𝑁 ∧ 𝑁 < (𝑁 + 1)) → 2 < (𝑁 + 1)))
20	16, 13, 18, 19	mp3an2i 1466	. . . . . . . . . . . . . . . 16 ⊢ (𝑁 ∈ ℕ → ((2 < 𝑁 ∧ 𝑁 < (𝑁 + 1)) → 2 < (𝑁 + 1)))
21	20	expdimp 453	. . . . . . . . . . . . . . 15 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → (𝑁 < (𝑁 + 1) → 2 < (𝑁 + 1)))
22	15, 21	mpd 15	. . . . . . . . . . . . . 14 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → 2 < (𝑁 + 1))
23	12, 22	eqbrtrid 5182	. . . . . . . . . . . . 13 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → (1 · 2) < (𝑁 + 1))
24		1red 11211	. . . . . . . . . . . . . 14 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → 1 ∈ ℝ)
25	18	adantr 481	. . . . . . . . . . . . . 14 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → (𝑁 + 1) ∈ ℝ)
26		2rp 12975	. . . . . . . . . . . . . . 15 ⊢ 2 ∈ ℝ⁺
27	26	a1i 11	. . . . . . . . . . . . . 14 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → 2 ∈ ℝ⁺)
28	24, 25, 27	ltmuldivd 13059	. . . . . . . . . . . . 13 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → ((1 · 2) < (𝑁 + 1) ↔ 1 < ((𝑁 + 1) / 2)))
29	23, 28	mpbid 231	. . . . . . . . . . . 12 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → 1 < ((𝑁 + 1) / 2))
30	18	rehalfcld 12455	. . . . . . . . . . . . . 14 ⊢ (𝑁 ∈ ℕ → ((𝑁 + 1) / 2) ∈ ℝ)
31	30	adantr 481	. . . . . . . . . . . . 13 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → ((𝑁 + 1) / 2) ∈ ℝ)
32	24, 31	posdifd 11797	. . . . . . . . . . . 12 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → (1 < ((𝑁 + 1) / 2) ↔ 0 < (((𝑁 + 1) / 2) − 1)))
33	29, 32	mpbid 231	. . . . . . . . . . 11 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → 0 < (((𝑁 + 1) / 2) − 1))
34	33	adantlr 713	. . . . . . . . . 10 ⊢ (((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) ∧ 2 < 𝑁) → 0 < (((𝑁 + 1) / 2) − 1))
35		elnnz 12564	. . . . . . . . . 10 ⊢ ((((𝑁 + 1) / 2) − 1) ∈ ℕ ↔ ((((𝑁 + 1) / 2) − 1) ∈ ℤ ∧ 0 < (((𝑁 + 1) / 2) − 1)))
36	10, 34, 35	sylanbrc 583	. . . . . . . . 9 ⊢ (((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) ∧ 2 < 𝑁) → (((𝑁 + 1) / 2) − 1) ∈ ℕ)
37		nncn 12216	. . . . . . . . . . . . 13 ⊢ (𝑁 ∈ ℕ → 𝑁 ∈ ℂ)
38		xp1d2m1eqxm1d2 12462	. . . . . . . . . . . . 13 ⊢ (𝑁 ∈ ℂ → (((𝑁 + 1) / 2) − 1) = ((𝑁 − 1) / 2))
39	37, 38	syl 17	. . . . . . . . . . . 12 ⊢ (𝑁 ∈ ℕ → (((𝑁 + 1) / 2) − 1) = ((𝑁 − 1) / 2))
40	39	eleq1d 2818	. . . . . . . . . . 11 ⊢ (𝑁 ∈ ℕ → ((((𝑁 + 1) / 2) − 1) ∈ ℕ ↔ ((𝑁 − 1) / 2) ∈ ℕ))
41	40	adantr 481	. . . . . . . . . 10 ⊢ ((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) → ((((𝑁 + 1) / 2) − 1) ∈ ℕ ↔ ((𝑁 − 1) / 2) ∈ ℕ))
42	41	adantr 481	. . . . . . . . 9 ⊢ (((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) ∧ 2 < 𝑁) → ((((𝑁 + 1) / 2) − 1) ∈ ℕ ↔ ((𝑁 − 1) / 2) ∈ ℕ))
43	36, 42	mpbid 231	. . . . . . . 8 ⊢ (((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) ∧ 2 < 𝑁) → ((𝑁 − 1) / 2) ∈ ℕ)
44	43	a1d 25	. . . . . . 7 ⊢ (((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) ∧ 2 < 𝑁) → (𝑁 ≠ 1 → ((𝑁 − 1) / 2) ∈ ℕ))
45	44	expcom 414	. . . . . 6 ⊢ (2 < 𝑁 → ((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) → (𝑁 ≠ 1 → ((𝑁 − 1) / 2) ∈ ℕ)))
46	6, 45	jaoi 855	. . . . 5 ⊢ ((𝑁 = 1 ∨ 2 < 𝑁) → ((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) → (𝑁 ≠ 1 → ((𝑁 − 1) / 2) ∈ ℕ)))
47	4, 46	mpcom 38	. . . 4 ⊢ ((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) → (𝑁 ≠ 1 → ((𝑁 − 1) / 2) ∈ ℕ))
48	47	impancom 452	. . 3 ⊢ ((𝑁 ∈ ℕ ∧ 𝑁 ≠ 1) → (((𝑁 + 1) / 2) ∈ ℕ₀ → ((𝑁 − 1) / 2) ∈ ℕ))
49	1, 48	sylbi 216	. 2 ⊢ (𝑁 ∈ (ℤ_≥‘2) → (((𝑁 + 1) / 2) ∈ ℕ₀ → ((𝑁 − 1) / 2) ∈ ℕ))
50	49	imp 407	1 ⊢ ((𝑁 ∈ (ℤ_≥‘2) ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) → ((𝑁 − 1) / 2) ∈ ℕ)

Colors of variables: wff setvar class

Syntax hints: → wi 4 ↔ wb 205 ∧ wa 396 ∨ wo 845 = wceq 1541 ∈ wcel 2106 ≠ wne 2940 class class class wbr 5147 ‘cfv 6540 (class class class)co 7405 ℂcc 11104 ℝcr 11105 0cc0 11106 1c1 11107 + caddc 11109 · cmul 11111 < clt 11244 − cmin 11440 / cdiv 11867 ℕcn 12208 2c2 12263 ℕ₀cn0 12468 ℤcz 12554 ℤ_≥cuz 12818 ℝ⁺crp 12970

This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1797 ax-4 1811 ax-5 1913 ax-6 1971 ax-7 2011 ax-8 2108 ax-9 2116 ax-10 2137 ax-11 2154 ax-12 2171 ax-ext 2703 ax-sep 5298 ax-nul 5305 ax-pow 5362 ax-pr 5426 ax-un 7721 ax-cnex 11162 ax-resscn 11163 ax-1cn 11164 ax-icn 11165 ax-addcl 11166 ax-addrcl 11167 ax-mulcl 11168 ax-mulrcl 11169 ax-mulcom 11170 ax-addass 11171 ax-mulass 11172 ax-distr 11173 ax-i2m1 11174 ax-1ne0 11175 ax-1rid 11176 ax-rnegex 11177 ax-rrecex 11178 ax-cnre 11179 ax-pre-lttri 11180 ax-pre-lttrn 11181 ax-pre-ltadd 11182 ax-pre-mulgt0 11183

This theorem depends on definitions: df-bi 206 df-an 397 df-or 846 df-3or 1088 df-3an 1089 df-tru 1544 df-fal 1554 df-ex 1782 df-nf 1786 df-sb 2068 df-mo 2534 df-eu 2563 df-clab 2710 df-cleq 2724 df-clel 2810 df-nfc 2885 df-ne 2941 df-nel 3047 df-ral 3062 df-rex 3071 df-rmo 3376 df-reu 3377 df-rab 3433 df-v 3476 df-sbc 3777 df-csb 3893 df-dif 3950 df-un 3952 df-in 3954 df-ss 3964 df-pss 3966 df-nul 4322 df-if 4528 df-pw 4603 df-sn 4628 df-pr 4630 df-op 4634 df-uni 4908 df-iun 4998 df-br 5148 df-opab 5210 df-mpt 5231 df-tr 5265 df-id 5573 df-eprel 5579 df-po 5587 df-so 5588 df-fr 5630 df-we 5632 df-xp 5681 df-rel 5682 df-cnv 5683 df-co 5684 df-dm 5685 df-rn 5686 df-res 5687 df-ima 5688 df-pred 6297 df-ord 6364 df-on 6365 df-lim 6366 df-suc 6367 df-iota 6492 df-fun 6542 df-fn 6543 df-f 6544 df-f1 6545 df-fo 6546 df-f1o 6547 df-fv 6548 df-riota 7361 df-ov 7408 df-oprab 7409 df-mpo 7410 df-om 7852 df-2nd 7972 df-frecs 8262 df-wrecs 8293 df-recs 8367 df-rdg 8406 df-er 8699 df-en 8936 df-dom 8937 df-sdom 8938 df-pnf 11246 df-mnf 11247 df-xr 11248 df-ltxr 11249 df-le 11250 df-sub 11442 df-neg 11443 df-div 11868 df-nn 12209 df-2 12271 df-3 12272 df-4 12273 df-n0 12469 df-z 12555 df-uz 12819 df-rp 12971

This theorem is referenced by: nn0o 16322 gausslemma2dlem0b 26849 blennngt2o2 47231 dignn0flhalf 47257

W3C validator