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Mirrors > Home > ILE Home > Th. List > fac1 | GIF version |
Description: The factorial of 1. (Contributed by NM, 2-Dec-2004.) (Revised by Mario Carneiro, 13-Jul-2013.) |
Ref | Expression |
---|---|
fac1 | ⊢ (!‘1) = 1 |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | 1nn 8050 | . . 3 ⊢ 1 ∈ ℕ | |
2 | facnn 9654 | . . 3 ⊢ (1 ∈ ℕ → (!‘1) = (seq1( · , I , ℂ)‘1)) | |
3 | 1, 2 | ax-mp 7 | . 2 ⊢ (!‘1) = (seq1( · , I , ℂ)‘1) |
4 | 1zzd 8378 | . . . 4 ⊢ (⊤ → 1 ∈ ℤ) | |
5 | cnex 7097 | . . . . 5 ⊢ ℂ ∈ V | |
6 | 5 | a1i 9 | . . . 4 ⊢ (⊤ → ℂ ∈ V) |
7 | fvi 5251 | . . . . . . . 8 ⊢ (𝑓 ∈ (ℤ≥‘1) → ( I ‘𝑓) = 𝑓) | |
8 | 7 | eleq1d 2147 | . . . . . . 7 ⊢ (𝑓 ∈ (ℤ≥‘1) → (( I ‘𝑓) ∈ (ℤ≥‘1) ↔ 𝑓 ∈ (ℤ≥‘1))) |
9 | 8 | ibir 175 | . . . . . 6 ⊢ (𝑓 ∈ (ℤ≥‘1) → ( I ‘𝑓) ∈ (ℤ≥‘1)) |
10 | eluzelcn 8630 | . . . . . 6 ⊢ (( I ‘𝑓) ∈ (ℤ≥‘1) → ( I ‘𝑓) ∈ ℂ) | |
11 | 9, 10 | syl 14 | . . . . 5 ⊢ (𝑓 ∈ (ℤ≥‘1) → ( I ‘𝑓) ∈ ℂ) |
12 | 11 | adantl 271 | . . . 4 ⊢ ((⊤ ∧ 𝑓 ∈ (ℤ≥‘1)) → ( I ‘𝑓) ∈ ℂ) |
13 | mulcl 7100 | . . . . 5 ⊢ ((𝑓 ∈ ℂ ∧ 𝑔 ∈ ℂ) → (𝑓 · 𝑔) ∈ ℂ) | |
14 | 13 | adantl 271 | . . . 4 ⊢ ((⊤ ∧ (𝑓 ∈ ℂ ∧ 𝑔 ∈ ℂ)) → (𝑓 · 𝑔) ∈ ℂ) |
15 | 4, 6, 12, 14 | iseq1 9442 | . . 3 ⊢ (⊤ → (seq1( · , I , ℂ)‘1) = ( I ‘1)) |
16 | 15 | trud 1293 | . 2 ⊢ (seq1( · , I , ℂ)‘1) = ( I ‘1) |
17 | fvi 5251 | . . 3 ⊢ (1 ∈ ℕ → ( I ‘1) = 1) | |
18 | 1, 17 | ax-mp 7 | . 2 ⊢ ( I ‘1) = 1 |
19 | 3, 16, 18 | 3eqtri 2105 | 1 ⊢ (!‘1) = 1 |
Colors of variables: wff set class |
Syntax hints: ∧ wa 102 = wceq 1284 ⊤wtru 1285 ∈ wcel 1433 Vcvv 2601 I cid 4043 ‘cfv 4922 (class class class)co 5532 ℂcc 6979 1c1 6982 · cmul 6986 ℕcn 8039 ℤ≥cuz 8619 seqcseq 9431 !cfa 9652 |
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 576 ax-in2 577 ax-io 662 ax-5 1376 ax-7 1377 ax-gen 1378 ax-ie1 1422 ax-ie2 1423 ax-8 1435 ax-10 1436 ax-11 1437 ax-i12 1438 ax-bndl 1439 ax-4 1440 ax-13 1444 ax-14 1445 ax-17 1459 ax-i9 1463 ax-ial 1467 ax-i5r 1468 ax-ext 2063 ax-coll 3893 ax-sep 3896 ax-nul 3904 ax-pow 3948 ax-pr 3964 ax-un 4188 ax-setind 4280 ax-iinf 4329 ax-cnex 7067 ax-resscn 7068 ax-1cn 7069 ax-1re 7070 ax-icn 7071 ax-addcl 7072 ax-addrcl 7073 ax-mulcl 7074 ax-addcom 7076 ax-addass 7078 ax-distr 7080 ax-i2m1 7081 ax-0lt1 7082 ax-0id 7084 ax-rnegex 7085 ax-cnre 7087 ax-pre-ltirr 7088 ax-pre-ltwlin 7089 ax-pre-lttrn 7090 ax-pre-ltadd 7092 |
This theorem depends on definitions: df-bi 115 df-3or 920 df-3an 921 df-tru 1287 df-fal 1290 df-nf 1390 df-sb 1686 df-eu 1944 df-mo 1945 df-clab 2068 df-cleq 2074 df-clel 2077 df-nfc 2208 df-ne 2246 df-nel 2340 df-ral 2353 df-rex 2354 df-reu 2355 df-rab 2357 df-v 2603 df-sbc 2816 df-csb 2909 df-dif 2975 df-un 2977 df-in 2979 df-ss 2986 df-nul 3252 df-pw 3384 df-sn 3404 df-pr 3405 df-op 3407 df-uni 3602 df-int 3637 df-iun 3680 df-br 3786 df-opab 3840 df-mpt 3841 df-tr 3876 df-id 4048 df-iord 4121 df-on 4123 df-suc 4126 df-iom 4332 df-xp 4369 df-rel 4370 df-cnv 4371 df-co 4372 df-dm 4373 df-rn 4374 df-res 4375 df-ima 4376 df-iota 4887 df-fun 4924 df-fn 4925 df-f 4926 df-f1 4927 df-fo 4928 df-f1o 4929 df-fv 4930 df-riota 5488 df-ov 5535 df-oprab 5536 df-mpt2 5537 df-1st 5787 df-2nd 5788 df-recs 5943 df-frec 6001 df-pnf 7155 df-mnf 7156 df-xr 7157 df-ltxr 7158 df-le 7159 df-sub 7281 df-neg 7282 df-inn 8040 df-n0 8289 df-z 8352 df-uz 8620 df-iseq 9432 df-fac 9653 |
This theorem is referenced by: facp1 9657 fac2 9658 bcn1 9685 |
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