fouriercnp - Mathbox for Glauco Siliprandi

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Theorem fouriercnp 47057

Description: If 𝐹 is continuous at the point 𝑋, then its Fourier series at 𝑋, converges to (𝐹‘𝑋). (Contributed by Glauco Siliprandi, 11-Dec-2019.)

**Hypotheses**
Ref	Expression
fouriercnp.f	⊢ (𝜑 → 𝐹:ℝ⟶ℝ)
fouriercnp.t	⊢ 𝑇 = (2 · π)
fouriercnp.per	⊢ ((𝜑 ∧ 𝑥 ∈ ℝ) → (𝐹‘(𝑥 + 𝑇)) = (𝐹‘𝑥))
fouriercnp.g	⊢ 𝐺 = ((ℝ D 𝐹) ↾ (-π(,)π))
fouriercnp.dmdv	⊢ (𝜑 → ((-π(,)π) ∖ dom 𝐺) ∈ Fin)
fouriercnp.dvcn	⊢ (𝜑 → 𝐺 ∈ (dom 𝐺–cn→ℂ))
fouriercnp.rlim	⊢ ((𝜑 ∧ 𝑥 ∈ ((-π[,)π) ∖ dom 𝐺)) → ((𝐺 ↾ (𝑥(,)+∞)) lim_ℂ 𝑥) ≠ ∅)
fouriercnp.llim	⊢ ((𝜑 ∧ 𝑥 ∈ ((-π(,]π) ∖ dom 𝐺)) → ((𝐺 ↾ (-∞(,)𝑥)) lim_ℂ 𝑥) ≠ ∅)
fouriercnp.j	⊢ 𝐽 = (topGen‘ran (,))
fouriercnp.cnp	⊢ (𝜑 → 𝐹 ∈ ((𝐽 CnP 𝐽)‘𝑋))
fouriercnp.a	⊢ 𝐴 = (𝑛 ∈ ℕ₀ ↦ (∫(-π(,)π)((𝐹‘𝑥) · (cos‘(𝑛 · 𝑥))) d𝑥 / π))
fouriercnp.b	⊢ 𝐵 = (𝑛 ∈ ℕ ↦ (∫(-π(,)π)((𝐹‘𝑥) · (sin‘(𝑛 · 𝑥))) d𝑥 / π))

**Assertion**
Ref	Expression
fouriercnp	⊢ (𝜑 → (((𝐴‘0) / 2) + Σ𝑛 ∈ ℕ (((𝐴‘𝑛) · (cos‘(𝑛 · 𝑋))) + ((𝐵‘𝑛) · (sin‘(𝑛 · 𝑋))))) = (𝐹‘𝑋))

Distinct variable groups: 𝑛,𝐹,𝑥 𝑥,𝐺 𝑥,𝑇 𝑛,𝑋,𝑥 𝜑,𝑥 Allowed substitution hints: 𝜑(𝑛) 𝐴(𝑥, 𝑛) 𝐵(𝑥, 𝑛) 𝑇(𝑛) 𝐺(𝑛) 𝐽(𝑥, 𝑛)

**Proof of Theorem fouriercnp**
Step	Hyp	Ref	Expression
1		fouriercnp.f	. . 3 ⊢ (𝜑 → 𝐹:ℝ⟶ℝ)
2		fouriercnp.t	. . 3 ⊢ 𝑇 = (2 · π)
3		fouriercnp.per	. . 3 ⊢ ((𝜑 ∧ 𝑥 ∈ ℝ) → (𝐹‘(𝑥 + 𝑇)) = (𝐹‘𝑥))
4		fouriercnp.g	. . 3 ⊢ 𝐺 = ((ℝ D 𝐹) ↾ (-π(,)π))
5		fouriercnp.dmdv	. . 3 ⊢ (𝜑 → ((-π(,)π) ∖ dom 𝐺) ∈ Fin)
6		fouriercnp.dvcn	. . 3 ⊢ (𝜑 → 𝐺 ∈ (dom 𝐺–cn→ℂ))
7		fouriercnp.rlim	. . 3 ⊢ ((𝜑 ∧ 𝑥 ∈ ((-π[,)π) ∖ dom 𝐺)) → ((𝐺 ↾ (𝑥(,)+∞)) lim_ℂ 𝑥) ≠ ∅)
8		fouriercnp.llim	. . 3 ⊢ ((𝜑 ∧ 𝑥 ∈ ((-π(,]π) ∖ dom 𝐺)) → ((𝐺 ↾ (-∞(,)𝑥)) lim_ℂ 𝑥) ≠ ∅)
9		fouriercnp.cnp	. . . 4 ⊢ (𝜑 → 𝐹 ∈ ((𝐽 CnP 𝐽)‘𝑋))
10		uniretop 24991	. . . . . 6 ⊢ ℝ = ∪ (topGen‘ran (,))
11		fouriercnp.j	. . . . . . 7 ⊢ 𝐽 = (topGen‘ran (,))
12	11	unieqi 4879	. . . . . 6 ⊢ ∪ 𝐽 = ∪ (topGen‘ran (,))
13	10, 12	eqtr4i 2786	. . . . 5 ⊢ ℝ = ∪ 𝐽
14	13	cnprcl 23473	. . . 4 ⊢ (𝐹 ∈ ((𝐽 CnP 𝐽)‘𝑋) → 𝑋 ∈ ℝ)
15	9, 14	syl 18	. . 3 ⊢ (𝜑 → 𝑋 ∈ ℝ)
16		limcresi 26115	. . . 4 ⊢ (𝐹 lim_ℂ 𝑋) ⊆ ((𝐹 ↾ (-∞(,)𝑋)) lim_ℂ 𝑋)
17		tgioo4 25034	. . . . . . . . . . 11 ⊢ (topGen‘ran (,)) = ((TopOpen‘ℂ_fld) ↾_t ℝ)
18	11, 17	eqtri 2783	. . . . . . . . . 10 ⊢ 𝐽 = ((TopOpen‘ℂ_fld) ↾_t ℝ)
19	18	oveq2i 7425	. . . . . . . . 9 ⊢ (𝐽 CnP 𝐽) = (𝐽 CnP ((TopOpen‘ℂ_fld) ↾_t ℝ))
20	19	fveq1i 6880	. . . . . . . 8 ⊢ ((𝐽 CnP 𝐽)‘𝑋) = ((𝐽 CnP ((TopOpen‘ℂ_fld) ↾_t ℝ))‘𝑋)
21	9, 20	eleqtrdi 2870	. . . . . . 7 ⊢ (𝜑 → 𝐹 ∈ ((𝐽 CnP ((TopOpen‘ℂ_fld) ↾_t ℝ))‘𝑋))
22		eqid 2760	. . . . . . . . . 10 ⊢ (TopOpen‘ℂ_fld) = (TopOpen‘ℂ_fld)
23	22	cnfldtop 25012	. . . . . . . . 9 ⊢ (TopOpen‘ℂ_fld) ∈ Top
24	23	a1i 11	. . . . . . . 8 ⊢ (𝜑 → (TopOpen‘ℂ_fld) ∈ Top)
25		ax-resscn 11184	. . . . . . . . 9 ⊢ ℝ ⊆ ℂ
26	25	a1i 11	. . . . . . . 8 ⊢ (𝜑 → ℝ ⊆ ℂ)
27		unicntop 25014	. . . . . . . . 9 ⊢ ℂ = ∪ (TopOpen‘ℂ_fld)
28	13, 27	cnprest2 23518	. . . . . . . 8 ⊢ (((TopOpen‘ℂ_fld) ∈ Top ∧ 𝐹:ℝ⟶ℝ ∧ ℝ ⊆ ℂ) → (𝐹 ∈ ((𝐽 CnP (TopOpen‘ℂ_fld))‘𝑋) ↔ 𝐹 ∈ ((𝐽 CnP ((TopOpen‘ℂ_fld) ↾_t ℝ))‘𝑋)))
29	24, 1, 26, 28	syl3anc 1398	. . . . . . 7 ⊢ (𝜑 → (𝐹 ∈ ((𝐽 CnP (TopOpen‘ℂ_fld))‘𝑋) ↔ 𝐹 ∈ ((𝐽 CnP ((TopOpen‘ℂ_fld) ↾_t ℝ))‘𝑋)))
30	21, 29	mpbird 260	. . . . . 6 ⊢ (𝜑 → 𝐹 ∈ ((𝐽 CnP (TopOpen‘ℂ_fld))‘𝑋))
31	22, 18	cnplimc 26117	. . . . . . 7 ⊢ ((ℝ ⊆ ℂ ∧ 𝑋 ∈ ℝ) → (𝐹 ∈ ((𝐽 CnP (TopOpen‘ℂ_fld))‘𝑋) ↔ (𝐹:ℝ⟶ℂ ∧ (𝐹‘𝑋) ∈ (𝐹 lim_ℂ 𝑋))))
32	25, 15, 31	sylancr 599	. . . . . 6 ⊢ (𝜑 → (𝐹 ∈ ((𝐽 CnP (TopOpen‘ℂ_fld))‘𝑋) ↔ (𝐹:ℝ⟶ℂ ∧ (𝐹‘𝑋) ∈ (𝐹 lim_ℂ 𝑋))))
33	30, 32	mpbid 235	. . . . 5 ⊢ (𝜑 → (𝐹:ℝ⟶ℂ ∧ (𝐹‘𝑋) ∈ (𝐹 lim_ℂ 𝑋)))
34	33	simprd 501	. . . 4 ⊢ (𝜑 → (𝐹‘𝑋) ∈ (𝐹 lim_ℂ 𝑋))
35	16, 34	sselid 3929	. . 3 ⊢ (𝜑 → (𝐹‘𝑋) ∈ ((𝐹 ↾ (-∞(,)𝑋)) lim_ℂ 𝑋))
36		limcresi 26115	. . . 4 ⊢ (𝐹 lim_ℂ 𝑋) ⊆ ((𝐹 ↾ (𝑋(,)+∞)) lim_ℂ 𝑋)
37	36, 34	sselid 3929	. . 3 ⊢ (𝜑 → (𝐹‘𝑋) ∈ ((𝐹 ↾ (𝑋(,)+∞)) lim_ℂ 𝑋))
38		fouriercnp.a	. . 3 ⊢ 𝐴 = (𝑛 ∈ ℕ₀ ↦ (∫(-π(,)π)((𝐹‘𝑥) · (cos‘(𝑛 · 𝑥))) d𝑥 / π))
39		fouriercnp.b	. . 3 ⊢ 𝐵 = (𝑛 ∈ ℕ ↦ (∫(-π(,)π)((𝐹‘𝑥) · (sin‘(𝑛 · 𝑥))) d𝑥 / π))
40	1, 2, 3, 4, 5, 6, 7, 8, 15, 35, 37, 38, 39	fourierd 47053	. 2 ⊢ (𝜑 → (((𝐴‘0) / 2) + Σ𝑛 ∈ ℕ (((𝐴‘𝑛) · (cos‘(𝑛 · 𝑋))) + ((𝐵‘𝑛) · (sin‘(𝑛 · 𝑋))))) = (((𝐹‘𝑋) + (𝐹‘𝑋)) / 2))
41	1, 15	ffvelcdmd 7079	. . . . . 6 ⊢ (𝜑 → (𝐹‘𝑋) ∈ ℝ)
42	41	recnd 11264	. . . . 5 ⊢ (𝜑 → (𝐹‘𝑋) ∈ ℂ)
43	42	2timesd 12514	. . . 4 ⊢ (𝜑 → (2 · (𝐹‘𝑋)) = ((𝐹‘𝑋) + (𝐹‘𝑋)))
44	43	eqcomd 2766	. . 3 ⊢ (𝜑 → ((𝐹‘𝑋) + (𝐹‘𝑋)) = (2 · (𝐹‘𝑋)))
45	44	oveq1d 7429	. 2 ⊢ (𝜑 → (((𝐹‘𝑋) + (𝐹‘𝑋)) / 2) = ((2 · (𝐹‘𝑋)) / 2))
46		2cnd 12346	. . 3 ⊢ (𝜑 → 2 ∈ ℂ)
47		2ne0 12374	. . . 4 ⊢ 2 ≠ 0
48	47	a1i 11	. . 3 ⊢ (𝜑 → 2 ≠ 0)
49	42, 46, 48	divcan3d 12023	. 2 ⊢ (𝜑 → ((2 · (𝐹‘𝑋)) / 2) = (𝐹‘𝑋))
50	40, 45, 49	3eqtrd 2799	1 ⊢ (𝜑 → (((𝐴‘0) / 2) + Σ𝑛 ∈ ℕ (((𝐴‘𝑛) · (cos‘(𝑛 · 𝑋))) + ((𝐵‘𝑛) · (sin‘(𝑛 · 𝑋))))) = (𝐹‘𝑋))

Colors of variables: wff setvar class

This proof depends on syntax axioms: → wi 4 ↔ wb 209 ∧ wa 401 = wceq 1570 ∈ wcel 2145 ≠ wne 2955 ∖ cdif 3896 ⊆ wss 3899 ∅c0 4279 ∪ cuni 4867 ↦ cmpt 5186 dom cdm 5655 ran crn 5656 ↾ cres 5657 ⟶wf 6529 ‘cfv 6533 (class class class)co 7414 Fincfn 8955 ℂcc 11125 ℝcr 11126 0cc0 11127 + caddc 11130 · cmul 11132 +∞cpnf 11267 -∞cmnf 11268 -cneg 11469 / cdiv 11898 ℕcn 12260 2c2 12322 ℕ₀cn0 12531 (,)cioo 13401 (,]cioc 13402 [,)cico 13403 Σcsu 15776 sincsin 16152 cosccos 16153 πcpi 16155 ↾_t crest 17508 TopOpenctopn 17509 topGenctg 17525 ℂ_fldccnfld 21588 Topctop 23121 CnP ccnp 23453 –cn→ccncf 25107 ∫citg 25849 lim_ℂ climc 26092 D cdv 26093

This proof depends on axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1828 ax-4 1842 ax-5 1943 ax-6 2000 ax-7 2041 ax-8 2147 ax-9 2155 ax-10 2178 ax-11 2194 ax-12 2213 ax-ext 2732 ax-rep 5232 ax-sep 5251 ax-nul 5263 ax-pow 5330 ax-pr 5398 ax-un 7737 ax-inf2 9623 ax-cc 10440 ax-cnex 11183 ax-resscn 11184 ax-1cn 11185 ax-icn 11186 ax-addcl 11187 ax-addrcl 11188 ax-mulcl 11189 ax-mulrcl 11190 ax-mulcom 11191 ax-addass 11192 ax-mulass 11193 ax-distr 11194 ax-i2m1 11195 ax-1ne0 11196 ax-1rid 11197 ax-rnegex 11198 ax-rrecex 11199 ax-cnre 11200 ax-pre-lttri 11201 ax-pre-lttrn 11202 ax-pre-ltadd 11203 ax-pre-mulgt0 11204 ax-pre-sup 11205 ax-addf 11206

This proof depends on definitions: df-bi 210 df-an 402 df-or 862 df-3or 1104 df-3an 1105 df-tru 1573 df-fal 1583 df-ex 1813 df-nf 1817 df-sb 2100 df-mo 2564 df-eu 2594 df-clab 2739 df-cleq 2752 df-clel 2835 df-nfc 2909 df-ne 2956 df-nel 3062 df-ral 3077 df-rex 3087 df-rmo 3365 df-reu 3366 df-rab 3413 df-v 3452 df-sbc 3740 df-csb 3848 df-dif 3902 df-un 3904 df-in 3906 df-ss 3916 df-pss 3919 df-symdif 4199 df-nul 4280 df-if 4483 df-pw 4559 df-sn 4585 df-pr 4587 df-tp 4589 df-op 4591 df-uni 4868 df-int 4908 df-iun 4953 df-iin 4954 df-disj 5071 df-br 5104 df-opab 5168 df-mpt 5187 df-tr 5213 df-id 5550 df-eprel 5555 df-po 5563 df-so 5564 df-fr 5608 df-se 5609 df-we 5610 df-xp 5661 df-rel 5662 df-cnv 5663 df-co 5664 df-dm 5665 df-rn 5666 df-res 5667 df-ima 5668 df-pred 6299 df-ord 6360 df-on 6361 df-lim 6362 df-suc 6363 df-iota 6489 df-fun 6535 df-fn 6536 df-f 6537 df-f1 6538 df-fo 6539 df-f1o 6540 df-fv 6541 df-isom 6542 df-riota 7371 df-ov 7417 df-oprab 7418 df-mpo 7419 df-of 7679 df-ofr 7680 df-om 7864 df-1st 7987 df-2nd 7988 df-supp 8160 df-frecs 8281 df-wrecs 8312 df-recs 8361 df-rdg 8400 df-1o 8458 df-2o 8459 df-oadd 8462 df-omul 8463 df-er 8699 df-map 8831 df-pm 8832 df-ixp 8908 df-en 8956 df-dom 8957 df-sdom 8958 df-fin 8959 df-fsupp 9335 df-fi 9384 df-sup 9415 df-inf 9416 df-oi 9485 df-dju 9909 df-card 9947 df-acn 9950 df-pnf 11272 df-mnf 11273 df-xr 11274 df-ltxr 11275 df-le 11276 df-sub 11470 df-neg 11471 df-div 11899 df-nn 12261 df-2 12330 df-3 12331 df-4 12332 df-5 12333 df-6 12334 df-7 12335 df-8 12336 df-9 12337 df-n0 12532 df-xnn0 12605 df-z 12619 df-dec 12740 df-uz 12891 df-q 13001 df-rp 13046 df-xneg 13166 df-xadd 13167 df-xmul 13168 df-ioo 13405 df-ioc 13406 df-ico 13407 df-icc 13408 df-fz 13565 df-fzo 13713 df-fl 13856 df-mod 13934 df-seq 14069 df-exp 14129 df-fac 14341 df-bc 14370 df-hash 14398 df-shft 15143 df-cj 15189 df-re 15190 df-im 15191 df-sqrt 15325 df-abs 15326 df-limsup 15561 df-clim 15578 df-rlim 15579 df-sum 15777 df-ef 16156 df-sin 16158 df-cos 16159 df-pi 16161 df-struct 17242 df-sets 17259 df-slot 17277 df-ndx 17289 df-base 17305 df-ress 17326 df-plusg 17358 df-mulr 17359 df-starv 17360 df-sca 17361 df-vsca 17362 df-ip 17363 df-tset 17364 df-ple 17365 df-ds 17367 df-unif 17368 df-hom 17369 df-cco 17370 df-rest 17510 df-topn 17511 df-0g 17529 df-gsum 17530 df-topgen 17531 df-pt 17532 df-prds 17535 df-xrs 17591 df-qtop 17596 df-imas 17597 df-xps 17599 df-mre 17673 df-mrc 17674 df-acs 17676 df-mgm 18733 df-sgrp 18824 df-mnd 18840 df-submnd 18895 df-mulg 19194 df-cntz 19447 df-cmn 19912 df-psmet 21580 df-xmet 21581 df-met 21582 df-bl 21583 df-mopn 21584 df-fbas 21585 df-fg 21586 df-cnfld 21589 df-top 23122 df-topon 23139 df-topsp 23161 df-bases 23174 df-cld 23247 df-ntr 23248 df-cls 23249 df-nei 23326 df-lp 23364 df-perf 23365 df-cn 23455 df-cnp 23456 df-t1 23542 df-haus 23543 df-cmp 23615 df-tx 23791 df-hmeo 23984 df-fil 24075 df-fm 24167 df-flim 24168 df-flf 24169 df-xms 24549 df-ms 24550 df-tms 24551 df-cncf 25109 df-ovol 25695 df-vol 25696 df-mbf 25850 df-itg1 25851 df-itg2 25852 df-ibl 25853 df-itg 25854 df-0p 25901 df-ditg 26077 df-limc 26096 df-dv 26097

This theorem is used by: fouriercn 47063

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