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Theorem nno 16352

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 12881	. . 3 ⊢ (𝑁 ∈ (ℤ_≥‘2) ↔ (𝑁 ∈ ℕ ∧ 𝑁 ≠ 1))
2		nnnn0 12449	. . . . . 6 ⊢ (𝑁 ∈ ℕ → 𝑁 ∈ ℕ₀)
3		nn0o1gt2 16351	. . . . . 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 2936	. . . . . . 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 12554	. . . . . . . . . . . 12 ⊢ (((𝑁 + 1) / 2) ∈ ℕ₀ → ((𝑁 + 1) / 2) ∈ ℤ)
8		peano2zm 12576	. . . . . . . . . . . 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 727	. . . . . . . . . 10 ⊢ (((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) ∧ 2 < 𝑁) → (((𝑁 + 1) / 2) − 1) ∈ ℤ)
11		2cn 12261	. . . . . . . . . . . . . . 15 ⊢ 2 ∈ ℂ
12	11	mullidi 11179	. . . . . . . . . . . . . 14 ⊢ (1 · 2) = 2
13		nnre 12193	. . . . . . . . . . . . . . . . 17 ⊢ (𝑁 ∈ ℕ → 𝑁 ∈ ℝ)
14	13	ltp1d 12113	. . . . . . . . . . . . . . . 16 ⊢ (𝑁 ∈ ℕ → 𝑁 < (𝑁 + 1))
15	14	adantr 480	. . . . . . . . . . . . . . 15 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → 𝑁 < (𝑁 + 1))
16		2re 12260	. . . . . . . . . . . . . . . . 17 ⊢ 2 ∈ ℝ
17		peano2nn 12198	. . . . . . . . . . . . . . . . . 18 ⊢ (𝑁 ∈ ℕ → (𝑁 + 1) ∈ ℕ)
18	17	nnred 12201	. . . . . . . . . . . . . . . . 17 ⊢ (𝑁 ∈ ℕ → (𝑁 + 1) ∈ ℝ)
19		lttr 11250	. . . . . . . . . . . . . . . . 17 ⊢ ((2 ∈ ℝ ∧ 𝑁 ∈ ℝ ∧ (𝑁 + 1) ∈ ℝ) → ((2 < 𝑁 ∧ 𝑁 < (𝑁 + 1)) → 2 < (𝑁 + 1)))
20	16, 13, 18, 19	mp3an2i 1468	. . . . . . . . . . . . . . . 16 ⊢ (𝑁 ∈ ℕ → ((2 < 𝑁 ∧ 𝑁 < (𝑁 + 1)) → 2 < (𝑁 + 1)))
21	20	expdimp 452	. . . . . . . . . . . . . . 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 5142	. . . . . . . . . . . . 13 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → (1 · 2) < (𝑁 + 1))
24		1red 11175	. . . . . . . . . . . . . 14 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → 1 ∈ ℝ)
25	18	adantr 480	. . . . . . . . . . . . . 14 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → (𝑁 + 1) ∈ ℝ)
26		2rp 12956	. . . . . . . . . . . . . . 15 ⊢ 2 ∈ ℝ⁺
27	26	a1i 11	. . . . . . . . . . . . . 14 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → 2 ∈ ℝ⁺)
28	24, 25, 27	ltmuldivd 13042	. . . . . . . . . . . . 13 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → ((1 · 2) < (𝑁 + 1) ↔ 1 < ((𝑁 + 1) / 2)))
29	23, 28	mpbid 232	. . . . . . . . . . . 12 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → 1 < ((𝑁 + 1) / 2))
30	18	rehalfcld 12429	. . . . . . . . . . . . . 14 ⊢ (𝑁 ∈ ℕ → ((𝑁 + 1) / 2) ∈ ℝ)
31	30	adantr 480	. . . . . . . . . . . . 13 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → ((𝑁 + 1) / 2) ∈ ℝ)
32	24, 31	posdifd 11765	. . . . . . . . . . . 12 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → (1 < ((𝑁 + 1) / 2) ↔ 0 < (((𝑁 + 1) / 2) − 1)))
33	29, 32	mpbid 232	. . . . . . . . . . 11 ⊢ ((𝑁 ∈ ℕ ∧ 2 < 𝑁) → 0 < (((𝑁 + 1) / 2) − 1))
34	33	adantlr 715	. . . . . . . . . 10 ⊢ (((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) ∧ 2 < 𝑁) → 0 < (((𝑁 + 1) / 2) − 1))
35		elnnz 12539	. . . . . . . . . 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 12194	. . . . . . . . . . . . 13 ⊢ (𝑁 ∈ ℕ → 𝑁 ∈ ℂ)
38		xp1d2m1eqxm1d2 12436	. . . . . . . . . . . . 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 2813	. . . . . . . . . . 11 ⊢ (𝑁 ∈ ℕ → ((((𝑁 + 1) / 2) − 1) ∈ ℕ ↔ ((𝑁 − 1) / 2) ∈ ℕ))
41	40	adantr 480	. . . . . . . . . 10 ⊢ ((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) → ((((𝑁 + 1) / 2) − 1) ∈ ℕ ↔ ((𝑁 − 1) / 2) ∈ ℕ))
42	41	adantr 480	. . . . . . . . 9 ⊢ (((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) ∧ 2 < 𝑁) → ((((𝑁 + 1) / 2) − 1) ∈ ℕ ↔ ((𝑁 − 1) / 2) ∈ ℕ))
43	36, 42	mpbid 232	. . . . . . . 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 413	. . . . . 6 ⊢ (2 < 𝑁 → ((𝑁 ∈ ℕ ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) → (𝑁 ≠ 1 → ((𝑁 − 1) / 2) ∈ ℕ)))
46	6, 45	jaoi 857	. . . . 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 451	. . 3 ⊢ ((𝑁 ∈ ℕ ∧ 𝑁 ≠ 1) → (((𝑁 + 1) / 2) ∈ ℕ₀ → ((𝑁 − 1) / 2) ∈ ℕ))
49	1, 48	sylbi 217	. 2 ⊢ (𝑁 ∈ (ℤ_≥‘2) → (((𝑁 + 1) / 2) ∈ ℕ₀ → ((𝑁 − 1) / 2) ∈ ℕ))
50	49	imp 406	1 ⊢ ((𝑁 ∈ (ℤ_≥‘2) ∧ ((𝑁 + 1) / 2) ∈ ℕ₀) → ((𝑁 − 1) / 2) ∈ ℕ)

Colors of variables: wff setvar class

Syntax hints: → wi 4 ↔ wb 206 ∧ wa 395 ∨ wo 847 = wceq 1540 ∈ wcel 2109 ≠ wne 2925 class class class wbr 5107 ‘cfv 6511 (class class class)co 7387 ℂcc 11066 ℝcr 11067 0cc0 11068 1c1 11069 + caddc 11071 · cmul 11073 < clt 11208 − cmin 11405 / cdiv 11835 ℕcn 12186 2c2 12241 ℕ₀cn0 12442 ℤcz 12529 ℤ_≥cuz 12793 ℝ⁺crp 12951

This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1795 ax-4 1809 ax-5 1910 ax-6 1967 ax-7 2008 ax-8 2111 ax-9 2119 ax-10 2142 ax-11 2158 ax-12 2178 ax-ext 2701 ax-sep 5251 ax-nul 5261 ax-pow 5320 ax-pr 5387 ax-un 7711 ax-cnex 11124 ax-resscn 11125 ax-1cn 11126 ax-icn 11127 ax-addcl 11128 ax-addrcl 11129 ax-mulcl 11130 ax-mulrcl 11131 ax-mulcom 11132 ax-addass 11133 ax-mulass 11134 ax-distr 11135 ax-i2m1 11136 ax-1ne0 11137 ax-1rid 11138 ax-rnegex 11139 ax-rrecex 11140 ax-cnre 11141 ax-pre-lttri 11142 ax-pre-lttrn 11143 ax-pre-ltadd 11144 ax-pre-mulgt0 11145

This theorem depends on definitions: df-bi 207 df-an 396 df-or 848 df-3or 1087 df-3an 1088 df-tru 1543 df-fal 1553 df-ex 1780 df-nf 1784 df-sb 2066 df-mo 2533 df-eu 2562 df-clab 2708 df-cleq 2721 df-clel 2803 df-nfc 2878 df-ne 2926 df-nel 3030 df-ral 3045 df-rex 3054 df-rmo 3354 df-reu 3355 df-rab 3406 df-v 3449 df-sbc 3754 df-csb 3863 df-dif 3917 df-un 3919 df-in 3921 df-ss 3931 df-pss 3934 df-nul 4297 df-if 4489 df-pw 4565 df-sn 4590 df-pr 4592 df-op 4596 df-uni 4872 df-iun 4957 df-br 5108 df-opab 5170 df-mpt 5189 df-tr 5215 df-id 5533 df-eprel 5538 df-po 5546 df-so 5547 df-fr 5591 df-we 5593 df-xp 5644 df-rel 5645 df-cnv 5646 df-co 5647 df-dm 5648 df-rn 5649 df-res 5650 df-ima 5651 df-pred 6274 df-ord 6335 df-on 6336 df-lim 6337 df-suc 6338 df-iota 6464 df-fun 6513 df-fn 6514 df-f 6515 df-f1 6516 df-fo 6517 df-f1o 6518 df-fv 6519 df-riota 7344 df-ov 7390 df-oprab 7391 df-mpo 7392 df-om 7843 df-2nd 7969 df-frecs 8260 df-wrecs 8291 df-recs 8340 df-rdg 8378 df-er 8671 df-en 8919 df-dom 8920 df-sdom 8921 df-pnf 11210 df-mnf 11211 df-xr 11212 df-ltxr 11213 df-le 11214 df-sub 11407 df-neg 11408 df-div 11836 df-nn 12187 df-2 12249 df-3 12250 df-4 12251 df-n0 12443 df-z 12530 df-uz 12794 df-rp 12952

This theorem is referenced by: nn0o 16353 gausslemma2dlem0b 27268 blennngt2o2 48581 dignn0flhalf 48607

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