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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 5252 | . . 3 ⊢ (𝑗 = 0 → (!‘𝑗) = (!‘0)) | |
2 | 1 | eleq1d 2151 | . 2 ⊢ (𝑗 = 0 → ((!‘𝑗) ∈ ℕ ↔ (!‘0) ∈ ℕ)) |
3 | fveq2 5252 | . . 3 ⊢ (𝑗 = 𝑘 → (!‘𝑗) = (!‘𝑘)) | |
4 | 3 | eleq1d 2151 | . 2 ⊢ (𝑗 = 𝑘 → ((!‘𝑗) ∈ ℕ ↔ (!‘𝑘) ∈ ℕ)) |
5 | fveq2 5252 | . . 3 ⊢ (𝑗 = (𝑘 + 1) → (!‘𝑗) = (!‘(𝑘 + 1))) | |
6 | 5 | eleq1d 2151 | . 2 ⊢ (𝑗 = (𝑘 + 1) → ((!‘𝑗) ∈ ℕ ↔ (!‘(𝑘 + 1)) ∈ ℕ)) |
7 | fveq2 5252 | . . 3 ⊢ (𝑗 = 𝑁 → (!‘𝑗) = (!‘𝑁)) | |
8 | 7 | eleq1d 2151 | . 2 ⊢ (𝑗 = 𝑁 → ((!‘𝑗) ∈ ℕ ↔ (!‘𝑁) ∈ ℕ)) |
9 | fac0 9970 | . . 3 ⊢ (!‘0) = 1 | |
10 | 1nn 8326 | . . 3 ⊢ 1 ∈ ℕ | |
11 | 9, 10 | eqeltri 2155 | . 2 ⊢ (!‘0) ∈ ℕ |
12 | facp1 9972 | . . . . 5 ⊢ (𝑘 ∈ ℕ0 → (!‘(𝑘 + 1)) = ((!‘𝑘) · (𝑘 + 1))) | |
13 | 12 | adantl 271 | . . . 4 ⊢ (((!‘𝑘) ∈ ℕ ∧ 𝑘 ∈ ℕ0) → (!‘(𝑘 + 1)) = ((!‘𝑘) · (𝑘 + 1))) |
14 | nn0p1nn 8603 | . . . . 5 ⊢ (𝑘 ∈ ℕ0 → (𝑘 + 1) ∈ ℕ) | |
15 | nnmulcl 8336 | . . . . 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 8755 | 1 ⊢ (𝑁 ∈ ℕ0 → (!‘𝑁) ∈ ℕ) |
Colors of variables: wff set class |
Syntax hints: → wi 4 ∧ wa 102 = wceq 1285 ∈ wcel 1434 ‘cfv 4968 (class class class)co 5590 0cc0 7252 1c1 7253 + caddc 7255 · cmul 7257 ℕcn 8315 ℕ0cn0 8564 !cfa 9967 |
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 3999 ax-un 4223 ax-setind 4315 ax-iinf 4365 ax-cnex 7338 ax-resscn 7339 ax-1cn 7340 ax-1re 7341 ax-icn 7342 ax-addcl 7343 ax-addrcl 7344 ax-mulcl 7345 ax-addcom 7347 ax-mulcom 7348 ax-addass 7349 ax-mulass 7350 ax-distr 7351 ax-i2m1 7352 ax-0lt1 7353 ax-1rid 7354 ax-0id 7355 ax-rnegex 7356 ax-cnre 7358 ax-pre-ltirr 7359 ax-pre-ltwlin 7360 ax-pre-lttrn 7361 ax-pre-ltadd 7363 |
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 4083 df-iord 4156 df-on 4158 df-ilim 4159 df-suc 4161 df-iom 4368 df-xp 4406 df-rel 4407 df-cnv 4408 df-co 4409 df-dm 4410 df-rn 4411 df-res 4412 df-ima 4413 df-iota 4933 df-fun 4970 df-fn 4971 df-f 4972 df-f1 4973 df-fo 4974 df-f1o 4975 df-fv 4976 df-riota 5546 df-ov 5593 df-oprab 5594 df-mpt2 5595 df-1st 5845 df-2nd 5846 df-recs 6001 df-frec 6087 df-pnf 7426 df-mnf 7427 df-xr 7428 df-ltxr 7429 df-le 7430 df-sub 7557 df-neg 7558 df-inn 8316 df-n0 8565 df-z 8646 df-uz 8914 df-iseq 9740 df-fac 9968 |
This theorem is referenced by: faccld 9978 facne0 9979 facdiv 9980 facndiv 9981 facwordi 9982 faclbnd 9983 faclbnd2 9984 faclbnd3 9985 faclbnd6 9986 facubnd 9987 facavg 9988 bcrpcl 9995 bcn0 9997 bcm1k 10002 permnn 10013 4bc2eq6 10016 dvdsfac 10640 prmfac1 10910 |
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