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Theorem facnn 14236

Description: Value of the factorial function for positive integers. (Contributed by NM, 2-Dec-2004.) (Revised by Mario Carneiro, 13-Jul-2013.)

**Assertion**
Ref	Expression
facnn	⊢ (𝑁 ∈ ℕ → (!‘𝑁) = (seq1( · , I )‘𝑁))

**Proof of Theorem facnn**
Step	Hyp	Ref	Expression
1		c0ex 11207	. . . 4 ⊢ 0 ∈ V
2	1	a1i 11	. . 3 ⊢ (𝑁 ∈ (ℕ₀ ∖ {0}) → 0 ∈ V)
3		1ex 11209	. . . 4 ⊢ 1 ∈ V
4	3	a1i 11	. . 3 ⊢ (𝑁 ∈ (ℕ₀ ∖ {0}) → 1 ∈ V)
5		df-fac 14235	. . . 4 ⊢ ! = ({⟨0, 1⟩} ∪ seq1( · , I ))
6		nnuz 12864	. . . . . . . 8 ⊢ ℕ = (ℤ_≥‘1)
7		dfn2 12484	. . . . . . . 8 ⊢ ℕ = (ℕ₀ ∖ {0})
8	6, 7	eqtr3i 2754	. . . . . . 7 ⊢ (ℤ_≥‘1) = (ℕ₀ ∖ {0})
9	8	reseq2i 5969	. . . . . 6 ⊢ (seq1( · , I ) ↾ (ℤ_≥‘1)) = (seq1( · , I ) ↾ (ℕ₀ ∖ {0}))
10		1z 12591	. . . . . . 7 ⊢ 1 ∈ ℤ
11		seqfn 13979	. . . . . . 7 ⊢ (1 ∈ ℤ → seq1( · , I ) Fn (ℤ_≥‘1))
12		fnresdm 6660	. . . . . . 7 ⊢ (seq1( · , I ) Fn (ℤ_≥‘1) → (seq1( · , I ) ↾ (ℤ_≥‘1)) = seq1( · , I ))
13	10, 11, 12	mp2b 10	. . . . . 6 ⊢ (seq1( · , I ) ↾ (ℤ_≥‘1)) = seq1( · , I )
14	9, 13	eqtr3i 2754	. . . . 5 ⊢ (seq1( · , I ) ↾ (ℕ₀ ∖ {0})) = seq1( · , I )
15	14	uneq2i 4153	. . . 4 ⊢ ({⟨0, 1⟩} ∪ (seq1( · , I ) ↾ (ℕ₀ ∖ {0}))) = ({⟨0, 1⟩} ∪ seq1( · , I ))
16	5, 15	eqtr4i 2755	. . 3 ⊢ ! = ({⟨0, 1⟩} ∪ (seq1( · , I ) ↾ (ℕ₀ ∖ {0})))
17		id 22	. . 3 ⊢ (𝑁 ∈ (ℕ₀ ∖ {0}) → 𝑁 ∈ (ℕ₀ ∖ {0}))
18	2, 4, 16, 17	fvsnun2 7174	. 2 ⊢ (𝑁 ∈ (ℕ₀ ∖ {0}) → (!‘𝑁) = (seq1( · , I )‘𝑁))
19	18, 7	eleq2s 2843	1 ⊢ (𝑁 ∈ ℕ → (!‘𝑁) = (seq1( · , I )‘𝑁))

Colors of variables: wff setvar class

Syntax hints: → wi 4 = wceq 1533 ∈ wcel 2098 Vcvv 3466 ∖ cdif 3938 ∪ cun 3939 {csn 4621 ⟨cop 4627 I cid 5564 ↾ cres 5669 Fn wfn 6529 ‘cfv 6534 0cc0 11107 1c1 11108 · cmul 11112 ℕcn 12211 ℕ₀cn0 12471 ℤcz 12557 ℤ_≥cuz 12821 seqcseq 13967 !cfa 14234

This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1789 ax-4 1803 ax-5 1905 ax-6 1963 ax-7 2003 ax-8 2100 ax-9 2108 ax-10 2129 ax-11 2146 ax-12 2163 ax-ext 2695 ax-sep 5290 ax-nul 5297 ax-pow 5354 ax-pr 5418 ax-un 7719 ax-cnex 11163 ax-resscn 11164 ax-1cn 11165 ax-icn 11166 ax-addcl 11167 ax-addrcl 11168 ax-mulcl 11169 ax-mulrcl 11170 ax-mulcom 11171 ax-addass 11172 ax-mulass 11173 ax-distr 11174 ax-i2m1 11175 ax-1ne0 11176 ax-1rid 11177 ax-rnegex 11178 ax-rrecex 11179 ax-cnre 11180 ax-pre-lttri 11181 ax-pre-lttrn 11182 ax-pre-ltadd 11183 ax-pre-mulgt0 11184

This theorem depends on definitions: df-bi 206 df-an 396 df-or 845 df-3or 1085 df-3an 1086 df-tru 1536 df-fal 1546 df-ex 1774 df-nf 1778 df-sb 2060 df-mo 2526 df-eu 2555 df-clab 2702 df-cleq 2716 df-clel 2802 df-nfc 2877 df-ne 2933 df-nel 3039 df-ral 3054 df-rex 3063 df-reu 3369 df-rab 3425 df-v 3468 df-sbc 3771 df-csb 3887 df-dif 3944 df-un 3946 df-in 3948 df-ss 3958 df-pss 3960 df-nul 4316 df-if 4522 df-pw 4597 df-sn 4622 df-pr 4624 df-op 4628 df-uni 4901 df-iun 4990 df-br 5140 df-opab 5202 df-mpt 5223 df-tr 5257 df-id 5565 df-eprel 5571 df-po 5579 df-so 5580 df-fr 5622 df-we 5624 df-xp 5673 df-rel 5674 df-cnv 5675 df-co 5676 df-dm 5677 df-rn 5678 df-res 5679 df-ima 5680 df-pred 6291 df-ord 6358 df-on 6359 df-lim 6360 df-suc 6361 df-iota 6486 df-fun 6536 df-fn 6537 df-f 6538 df-f1 6539 df-fo 6540 df-f1o 6541 df-fv 6542 df-riota 7358 df-ov 7405 df-oprab 7406 df-mpo 7407 df-om 7850 df-2nd 7970 df-frecs 8262 df-wrecs 8293 df-recs 8367 df-rdg 8406 df-er 8700 df-en 8937 df-dom 8938 df-sdom 8939 df-pnf 11249 df-mnf 11250 df-xr 11251 df-ltxr 11252 df-le 11253 df-sub 11445 df-neg 11446 df-nn 12212 df-n0 12472 df-z 12558 df-uz 12822 df-seq 13968 df-fac 14235

This theorem is referenced by: fac1 14238 facp1 14239 bcval5 14279 fprodfac 15919 logfac 26475 wilthlem3 26942

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