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Theorem fallfacval3 15720

Description: A product representation of falling factorial when 𝐴 is a nonnegative integer. (Contributed by Scott Fenton, 20-Mar-2018.)

**Assertion**
Ref	Expression
fallfacval3	⊢ (𝑁 ∈ (0...𝐴) → (𝐴 FallFac 𝑁) = ∏𝑘 ∈ ((𝐴 − (𝑁 − 1))...𝐴)𝑘)

Distinct variable groups: 𝐴,𝑘 𝑘,𝑁

Proof of Theorem fallfacval3 Dummy variable 𝑗 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		elfz3nn0 13348	. . . 4 ⊢ (𝑁 ∈ (0...𝐴) → 𝐴 ∈ ℕ₀)
2	1	nn0cnd 12293	. . 3 ⊢ (𝑁 ∈ (0...𝐴) → 𝐴 ∈ ℂ)
3		elfznn0 13347	. . 3 ⊢ (𝑁 ∈ (0...𝐴) → 𝑁 ∈ ℕ₀)
4		fallfacval 15717	. . 3 ⊢ ((𝐴 ∈ ℂ ∧ 𝑁 ∈ ℕ₀) → (𝐴 FallFac 𝑁) = ∏𝑗 ∈ (0...(𝑁 − 1))(𝐴 − 𝑗))
5	2, 3, 4	syl2anc 584	. 2 ⊢ (𝑁 ∈ (0...𝐴) → (𝐴 FallFac 𝑁) = ∏𝑗 ∈ (0...(𝑁 − 1))(𝐴 − 𝑗))
6		elfzel2 13252	. . 3 ⊢ (𝑁 ∈ (0...𝐴) → 𝐴 ∈ ℤ)
7		elfzel1 13253	. . 3 ⊢ (𝑁 ∈ (0...𝐴) → 0 ∈ ℤ)
8		elfzelz 13254	. . . 4 ⊢ (𝑁 ∈ (0...𝐴) → 𝑁 ∈ ℤ)
9		peano2zm 12361	. . . 4 ⊢ (𝑁 ∈ ℤ → (𝑁 − 1) ∈ ℤ)
10	8, 9	syl 17	. . 3 ⊢ (𝑁 ∈ (0...𝐴) → (𝑁 − 1) ∈ ℤ)
11		elfzelz 13254	. . . . 5 ⊢ (𝑗 ∈ (0...(𝑁 − 1)) → 𝑗 ∈ ℤ)
12	11	zcnd 12425	. . . 4 ⊢ (𝑗 ∈ (0...(𝑁 − 1)) → 𝑗 ∈ ℂ)
13		subcl 11218	. . . 4 ⊢ ((𝐴 ∈ ℂ ∧ 𝑗 ∈ ℂ) → (𝐴 − 𝑗) ∈ ℂ)
14	2, 12, 13	syl2an 596	. . 3 ⊢ ((𝑁 ∈ (0...𝐴) ∧ 𝑗 ∈ (0...(𝑁 − 1))) → (𝐴 − 𝑗) ∈ ℂ)
15		oveq2 7285	. . 3 ⊢ (𝑗 = (𝐴 − 𝑘) → (𝐴 − 𝑗) = (𝐴 − (𝐴 − 𝑘)))
16	6, 7, 10, 14, 15	fprodrev 15685	. 2 ⊢ (𝑁 ∈ (0...𝐴) → ∏𝑗 ∈ (0...(𝑁 − 1))(𝐴 − 𝑗) = ∏𝑘 ∈ ((𝐴 − (𝑁 − 1))...(𝐴 − 0))(𝐴 − (𝐴 − 𝑘)))
17	2	subid1d 11319	. . . 4 ⊢ (𝑁 ∈ (0...𝐴) → (𝐴 − 0) = 𝐴)
18	17	oveq2d 7293	. . 3 ⊢ (𝑁 ∈ (0...𝐴) → ((𝐴 − (𝑁 − 1))...(𝐴 − 0)) = ((𝐴 − (𝑁 − 1))...𝐴))
19	2	adantr 481	. . . 4 ⊢ ((𝑁 ∈ (0...𝐴) ∧ 𝑘 ∈ ((𝐴 − (𝑁 − 1))...(𝐴 − 0))) → 𝐴 ∈ ℂ)
20		elfzelz 13254	. . . . . 6 ⊢ (𝑘 ∈ ((𝐴 − (𝑁 − 1))...(𝐴 − 0)) → 𝑘 ∈ ℤ)
21	20	zcnd 12425	. . . . 5 ⊢ (𝑘 ∈ ((𝐴 − (𝑁 − 1))...(𝐴 − 0)) → 𝑘 ∈ ℂ)
22	21	adantl 482	. . . 4 ⊢ ((𝑁 ∈ (0...𝐴) ∧ 𝑘 ∈ ((𝐴 − (𝑁 − 1))...(𝐴 − 0))) → 𝑘 ∈ ℂ)
23	19, 22	nncand 11335	. . 3 ⊢ ((𝑁 ∈ (0...𝐴) ∧ 𝑘 ∈ ((𝐴 − (𝑁 − 1))...(𝐴 − 0))) → (𝐴 − (𝐴 − 𝑘)) = 𝑘)
24	18, 23	prodeq12dv 15634	. 2 ⊢ (𝑁 ∈ (0...𝐴) → ∏𝑘 ∈ ((𝐴 − (𝑁 − 1))...(𝐴 − 0))(𝐴 − (𝐴 − 𝑘)) = ∏𝑘 ∈ ((𝐴 − (𝑁 − 1))...𝐴)𝑘)
25	5, 16, 24	3eqtrd 2782	1 ⊢ (𝑁 ∈ (0...𝐴) → (𝐴 FallFac 𝑁) = ∏𝑘 ∈ ((𝐴 − (𝑁 − 1))...𝐴)𝑘)

Colors of variables: wff setvar class

Syntax hints: → wi 4 ∧ wa 396 = wceq 1539 ∈ wcel 2106 (class class class)co 7277 ℂcc 10867 0cc0 10869 1c1 10870 − cmin 11203 ℕ₀cn0 12231 ℤcz 12317 ...cfz 13237 ∏cprod 15613 FallFac cfallfac 15712

This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1798 ax-4 1812 ax-5 1913 ax-6 1971 ax-7 2011 ax-8 2108 ax-9 2116 ax-10 2137 ax-11 2154 ax-12 2171 ax-ext 2709 ax-rep 5211 ax-sep 5225 ax-nul 5232 ax-pow 5290 ax-pr 5354 ax-un 7588 ax-inf2 9397 ax-cnex 10925 ax-resscn 10926 ax-1cn 10927 ax-icn 10928 ax-addcl 10929 ax-addrcl 10930 ax-mulcl 10931 ax-mulrcl 10932 ax-mulcom 10933 ax-addass 10934 ax-mulass 10935 ax-distr 10936 ax-i2m1 10937 ax-1ne0 10938 ax-1rid 10939 ax-rnegex 10940 ax-rrecex 10941 ax-cnre 10942 ax-pre-lttri 10943 ax-pre-lttrn 10944 ax-pre-ltadd 10945 ax-pre-mulgt0 10946 ax-pre-sup 10947

This theorem depends on definitions: df-bi 206 df-an 397 df-or 845 df-3or 1087 df-3an 1088 df-tru 1542 df-fal 1552 df-ex 1783 df-nf 1787 df-sb 2068 df-mo 2540 df-eu 2569 df-clab 2716 df-cleq 2730 df-clel 2816 df-nfc 2889 df-ne 2944 df-nel 3050 df-ral 3069 df-rex 3070 df-rmo 3071 df-reu 3072 df-rab 3073 df-v 3433 df-sbc 3718 df-csb 3834 df-dif 3891 df-un 3893 df-in 3895 df-ss 3905 df-pss 3907 df-nul 4259 df-if 4462 df-pw 4537 df-sn 4564 df-pr 4566 df-op 4570 df-uni 4842 df-int 4882 df-iun 4928 df-br 5077 df-opab 5139 df-mpt 5160 df-tr 5194 df-id 5491 df-eprel 5497 df-po 5505 df-so 5506 df-fr 5546 df-se 5547 df-we 5548 df-xp 5597 df-rel 5598 df-cnv 5599 df-co 5600 df-dm 5601 df-rn 5602 df-res 5603 df-ima 5604 df-pred 6204 df-ord 6271 df-on 6272 df-lim 6273 df-suc 6274 df-iota 6393 df-fun 6437 df-fn 6438 df-f 6439 df-f1 6440 df-fo 6441 df-f1o 6442 df-fv 6443 df-isom 6444 df-riota 7234 df-ov 7280 df-oprab 7281 df-mpo 7282 df-om 7713 df-1st 7831 df-2nd 7832 df-frecs 8095 df-wrecs 8126 df-recs 8200 df-rdg 8239 df-1o 8295 df-er 8496 df-en 8732 df-dom 8733 df-sdom 8734 df-fin 8735 df-sup 9199 df-oi 9267 df-card 9695 df-pnf 11009 df-mnf 11010 df-xr 11011 df-ltxr 11012 df-le 11013 df-sub 11205 df-neg 11206 df-div 11631 df-nn 11972 df-2 12034 df-3 12035 df-n0 12232 df-z 12318 df-uz 12581 df-rp 12729 df-fz 13238 df-fzo 13381 df-seq 13720 df-exp 13781 df-hash 14043 df-cj 14808 df-re 14809 df-im 14810 df-sqrt 14944 df-abs 14945 df-clim 15195 df-prod 15614 df-fallfac 15715

This theorem is referenced by: fallfacval4 15751

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