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Mirrors > Home > ILE Home > Th. List > faccl | GIF version |
Description: Closure of the factorial function. (Contributed by NM, 2-Dec-2004.) |
Ref | Expression |
---|---|
faccl | ⊢ (𝑁 ∈ ℕ0 → (!‘𝑁) ∈ ℕ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | fveq2 5253 | . . 3 ⊢ (𝑗 = 0 → (!‘𝑗) = (!‘0)) | |
2 | 1 | eleq1d 2151 | . 2 ⊢ (𝑗 = 0 → ((!‘𝑗) ∈ ℕ ↔ (!‘0) ∈ ℕ)) |
3 | fveq2 5253 | . . 3 ⊢ (𝑗 = 𝑘 → (!‘𝑗) = (!‘𝑘)) | |
4 | 3 | eleq1d 2151 | . 2 ⊢ (𝑗 = 𝑘 → ((!‘𝑗) ∈ ℕ ↔ (!‘𝑘) ∈ ℕ)) |
5 | fveq2 5253 | . . 3 ⊢ (𝑗 = (𝑘 + 1) → (!‘𝑗) = (!‘(𝑘 + 1))) | |
6 | 5 | eleq1d 2151 | . 2 ⊢ (𝑗 = (𝑘 + 1) → ((!‘𝑗) ∈ ℕ ↔ (!‘(𝑘 + 1)) ∈ ℕ)) |
7 | fveq2 5253 | . . 3 ⊢ (𝑗 = 𝑁 → (!‘𝑗) = (!‘𝑁)) | |
8 | 7 | eleq1d 2151 | . 2 ⊢ (𝑗 = 𝑁 → ((!‘𝑗) ∈ ℕ ↔ (!‘𝑁) ∈ ℕ)) |
9 | fac0 9971 | . . 3 ⊢ (!‘0) = 1 | |
10 | 1nn 8327 | . . 3 ⊢ 1 ∈ ℕ | |
11 | 9, 10 | eqeltri 2155 | . 2 ⊢ (!‘0) ∈ ℕ |
12 | facp1 9973 | . . . . 5 ⊢ (𝑘 ∈ ℕ0 → (!‘(𝑘 + 1)) = ((!‘𝑘) · (𝑘 + 1))) | |
13 | 12 | adantl 271 | . . . 4 ⊢ (((!‘𝑘) ∈ ℕ ∧ 𝑘 ∈ ℕ0) → (!‘(𝑘 + 1)) = ((!‘𝑘) · (𝑘 + 1))) |
14 | nn0p1nn 8604 | . . . . 5 ⊢ (𝑘 ∈ ℕ0 → (𝑘 + 1) ∈ ℕ) | |
15 | nnmulcl 8337 | . . . . 5 ⊢ (((!‘𝑘) ∈ ℕ ∧ (𝑘 + 1) ∈ ℕ) → ((!‘𝑘) · (𝑘 + 1)) ∈ ℕ) | |
16 | 14, 15 | sylan2 280 | . . . 4 ⊢ (((!‘𝑘) ∈ ℕ ∧ 𝑘 ∈ ℕ0) → ((!‘𝑘) · (𝑘 + 1)) ∈ ℕ) |
17 | 13, 16 | eqeltrd 2159 | . . 3 ⊢ (((!‘𝑘) ∈ ℕ ∧ 𝑘 ∈ ℕ0) → (!‘(𝑘 + 1)) ∈ ℕ) |
18 | 17 | expcom 114 | . 2 ⊢ (𝑘 ∈ ℕ0 → ((!‘𝑘) ∈ ℕ → (!‘(𝑘 + 1)) ∈ ℕ)) |
19 | 2, 4, 6, 8, 11, 18 | nn0ind 8756 | 1 ⊢ (𝑁 ∈ ℕ0 → (!‘𝑁) ∈ ℕ) |
Colors of variables: wff set class |
Syntax hints: → wi 4 ∧ wa 102 = wceq 1285 ∈ wcel 1434 ‘cfv 4969 (class class class)co 5591 0cc0 7253 1c1 7254 + caddc 7256 · cmul 7258 ℕcn 8316 ℕ0cn0 8565 !cfa 9968 |
This theorem was proved from axioms: ax-1 5 ax-2 6 ax-mp 7 ax-ia1 104 ax-ia2 105 ax-ia3 106 ax-in1 577 ax-in2 578 ax-io 663 ax-5 1377 ax-7 1378 ax-gen 1379 ax-ie1 1423 ax-ie2 1424 ax-8 1436 ax-10 1437 ax-11 1438 ax-i12 1439 ax-bndl 1440 ax-4 1441 ax-13 1445 ax-14 1446 ax-17 1460 ax-i9 1464 ax-ial 1468 ax-i5r 1469 ax-ext 2065 ax-coll 3919 ax-sep 3922 ax-nul 3930 ax-pow 3974 ax-pr 4000 ax-un 4224 ax-setind 4316 ax-iinf 4366 ax-cnex 7339 ax-resscn 7340 ax-1cn 7341 ax-1re 7342 ax-icn 7343 ax-addcl 7344 ax-addrcl 7345 ax-mulcl 7346 ax-addcom 7348 ax-mulcom 7349 ax-addass 7350 ax-mulass 7351 ax-distr 7352 ax-i2m1 7353 ax-0lt1 7354 ax-1rid 7355 ax-0id 7356 ax-rnegex 7357 ax-cnre 7359 ax-pre-ltirr 7360 ax-pre-ltwlin 7361 ax-pre-lttrn 7362 ax-pre-ltadd 7364 |
This theorem depends on definitions: df-bi 115 df-3or 921 df-3an 922 df-tru 1288 df-fal 1291 df-nf 1391 df-sb 1688 df-eu 1946 df-mo 1947 df-clab 2070 df-cleq 2076 df-clel 2079 df-nfc 2212 df-ne 2250 df-nel 2345 df-ral 2358 df-rex 2359 df-reu 2360 df-rab 2362 df-v 2614 df-sbc 2827 df-csb 2920 df-dif 2986 df-un 2988 df-in 2990 df-ss 2997 df-nul 3270 df-pw 3408 df-sn 3428 df-pr 3429 df-op 3431 df-uni 3628 df-int 3663 df-iun 3706 df-br 3812 df-opab 3866 df-mpt 3867 df-tr 3902 df-id 4084 df-iord 4157 df-on 4159 df-ilim 4160 df-suc 4162 df-iom 4369 df-xp 4407 df-rel 4408 df-cnv 4409 df-co 4410 df-dm 4411 df-rn 4412 df-res 4413 df-ima 4414 df-iota 4934 df-fun 4971 df-fn 4972 df-f 4973 df-f1 4974 df-fo 4975 df-f1o 4976 df-fv 4977 df-riota 5547 df-ov 5594 df-oprab 5595 df-mpt2 5596 df-1st 5846 df-2nd 5847 df-recs 6002 df-frec 6088 df-pnf 7427 df-mnf 7428 df-xr 7429 df-ltxr 7430 df-le 7431 df-sub 7558 df-neg 7559 df-inn 8317 df-n0 8566 df-z 8647 df-uz 8915 df-iseq 9741 df-fac 9969 |
This theorem is referenced by: faccld 9979 facne0 9980 facdiv 9981 facndiv 9982 facwordi 9983 faclbnd 9984 faclbnd2 9985 faclbnd3 9986 faclbnd6 9987 facubnd 9988 facavg 9989 bcrpcl 9996 bcn0 9998 bcm1k 10003 permnn 10014 4bc2eq6 10017 dvdsfac 10641 prmfac1 10911 |
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