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Mirrors > Home > ILE Home > Th. List > nnesq | GIF version |
Description: A positive integer is even iff its square is even. (Contributed by NM, 20-Aug-2001.) (Revised by Mario Carneiro, 12-Sep-2015.) |
Ref | Expression |
---|---|
nnesq | ⊢ (𝑁 ∈ ℕ → ((𝑁 / 2) ∈ ℕ ↔ ((𝑁↑2) / 2) ∈ ℕ)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | nnz 9201 | . . . 4 ⊢ (𝑁 ∈ ℕ → 𝑁 ∈ ℤ) | |
2 | zesq 10562 | . . . 4 ⊢ (𝑁 ∈ ℤ → ((𝑁 / 2) ∈ ℤ ↔ ((𝑁↑2) / 2) ∈ ℤ)) | |
3 | 1, 2 | syl 14 | . . 3 ⊢ (𝑁 ∈ ℕ → ((𝑁 / 2) ∈ ℤ ↔ ((𝑁↑2) / 2) ∈ ℤ)) |
4 | nnrp 9590 | . . . . . 6 ⊢ (𝑁 ∈ ℕ → 𝑁 ∈ ℝ+) | |
5 | 4 | rphalfcld 9636 | . . . . 5 ⊢ (𝑁 ∈ ℕ → (𝑁 / 2) ∈ ℝ+) |
6 | 5 | rpgt0d 9626 | . . . 4 ⊢ (𝑁 ∈ ℕ → 0 < (𝑁 / 2)) |
7 | nnsqcl 10514 | . . . . . . 7 ⊢ (𝑁 ∈ ℕ → (𝑁↑2) ∈ ℕ) | |
8 | 7 | nnrpd 9621 | . . . . . 6 ⊢ (𝑁 ∈ ℕ → (𝑁↑2) ∈ ℝ+) |
9 | 8 | rphalfcld 9636 | . . . . 5 ⊢ (𝑁 ∈ ℕ → ((𝑁↑2) / 2) ∈ ℝ+) |
10 | 9 | rpgt0d 9626 | . . . 4 ⊢ (𝑁 ∈ ℕ → 0 < ((𝑁↑2) / 2)) |
11 | 6, 10 | 2thd 174 | . . 3 ⊢ (𝑁 ∈ ℕ → (0 < (𝑁 / 2) ↔ 0 < ((𝑁↑2) / 2))) |
12 | 3, 11 | anbi12d 465 | . 2 ⊢ (𝑁 ∈ ℕ → (((𝑁 / 2) ∈ ℤ ∧ 0 < (𝑁 / 2)) ↔ (((𝑁↑2) / 2) ∈ ℤ ∧ 0 < ((𝑁↑2) / 2)))) |
13 | elnnz 9192 | . 2 ⊢ ((𝑁 / 2) ∈ ℕ ↔ ((𝑁 / 2) ∈ ℤ ∧ 0 < (𝑁 / 2))) | |
14 | elnnz 9192 | . 2 ⊢ (((𝑁↑2) / 2) ∈ ℕ ↔ (((𝑁↑2) / 2) ∈ ℤ ∧ 0 < ((𝑁↑2) / 2))) | |
15 | 12, 13, 14 | 3bitr4g 222 | 1 ⊢ (𝑁 ∈ ℕ → ((𝑁 / 2) ∈ ℕ ↔ ((𝑁↑2) / 2) ∈ ℕ)) |
Colors of variables: wff set class |
Syntax hints: → wi 4 ∧ wa 103 ↔ wb 104 ∈ wcel 2135 class class class wbr 3976 (class class class)co 5836 0cc0 7744 < clt 7924 / cdiv 8559 ℕcn 8848 2c2 8899 ℤcz 9182 ↑cexp 10444 |
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 604 ax-in2 605 ax-io 699 ax-5 1434 ax-7 1435 ax-gen 1436 ax-ie1 1480 ax-ie2 1481 ax-8 1491 ax-10 1492 ax-11 1493 ax-i12 1494 ax-bndl 1496 ax-4 1497 ax-17 1513 ax-i9 1517 ax-ial 1521 ax-i5r 1522 ax-13 2137 ax-14 2138 ax-ext 2146 ax-coll 4091 ax-sep 4094 ax-nul 4102 ax-pow 4147 ax-pr 4181 ax-un 4405 ax-setind 4508 ax-iinf 4559 ax-cnex 7835 ax-resscn 7836 ax-1cn 7837 ax-1re 7838 ax-icn 7839 ax-addcl 7840 ax-addrcl 7841 ax-mulcl 7842 ax-mulrcl 7843 ax-addcom 7844 ax-mulcom 7845 ax-addass 7846 ax-mulass 7847 ax-distr 7848 ax-i2m1 7849 ax-0lt1 7850 ax-1rid 7851 ax-0id 7852 ax-rnegex 7853 ax-precex 7854 ax-cnre 7855 ax-pre-ltirr 7856 ax-pre-ltwlin 7857 ax-pre-lttrn 7858 ax-pre-apti 7859 ax-pre-ltadd 7860 ax-pre-mulgt0 7861 ax-pre-mulext 7862 |
This theorem depends on definitions: df-bi 116 df-dc 825 df-3or 968 df-3an 969 df-tru 1345 df-fal 1348 df-nf 1448 df-sb 1750 df-eu 2016 df-mo 2017 df-clab 2151 df-cleq 2157 df-clel 2160 df-nfc 2295 df-ne 2335 df-nel 2430 df-ral 2447 df-rex 2448 df-reu 2449 df-rmo 2450 df-rab 2451 df-v 2723 df-sbc 2947 df-csb 3041 df-dif 3113 df-un 3115 df-in 3117 df-ss 3124 df-nul 3405 df-if 3516 df-pw 3555 df-sn 3576 df-pr 3577 df-op 3579 df-uni 3784 df-int 3819 df-iun 3862 df-br 3977 df-opab 4038 df-mpt 4039 df-tr 4075 df-id 4265 df-po 4268 df-iso 4269 df-iord 4338 df-on 4340 df-ilim 4341 df-suc 4343 df-iom 4562 df-xp 4604 df-rel 4605 df-cnv 4606 df-co 4607 df-dm 4608 df-rn 4609 df-res 4610 df-ima 4611 df-iota 5147 df-fun 5184 df-fn 5185 df-f 5186 df-f1 5187 df-fo 5188 df-f1o 5189 df-fv 5190 df-riota 5792 df-ov 5839 df-oprab 5840 df-mpo 5841 df-1st 6100 df-2nd 6101 df-recs 6264 df-frec 6350 df-pnf 7926 df-mnf 7927 df-xr 7928 df-ltxr 7929 df-le 7930 df-sub 8062 df-neg 8063 df-reap 8464 df-ap 8471 df-div 8560 df-inn 8849 df-2 8907 df-n0 9106 df-z 9183 df-uz 9458 df-rp 9581 df-seqfrec 10371 df-exp 10445 |
This theorem is referenced by: sqrt2irrlem 12072 |
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