![]() |
Mathbox for Glauco Siliprandi |
< Previous
Next >
Nearby theorems |
|
Mirrors > Home > MPE Home > Th. List > Mathboxes > stowei | Structured version Visualization version GIF version |
Description: This theorem proves the Stone-Weierstrass theorem for real-valued functions: let 𝐽 be a compact topology on 𝑇, and 𝐶 be the set of real continuous functions on 𝑇. Assume that 𝐴 is a subalgebra of 𝐶 (closed under addition and multiplication of functions) containing constant functions and discriminating points (if 𝑟 and 𝑡 are distinct points in 𝑇, then there exists a function ℎ in 𝐴 such that h(r) is distinct from h(t) ). Then, for any continuous function 𝐹 and for any positive real 𝐸, there exists a function 𝑓 in the subalgebra 𝐴, such that 𝑓 approximates 𝐹 up to 𝐸 (𝐸 represents the usual ε value). As a classical example, given any a, b reals, the closed interval 𝑇 = [𝑎, 𝑏] could be taken, along with the subalgebra 𝐴 of real polynomials on 𝑇, and then use this theorem to easily prove that real polynomials are dense in the standard metric space of continuous functions on [𝑎, 𝑏]. The proof and lemmas are written following [BrosowskiDeutsh] p. 89 (through page 92). Some effort is put in avoiding the use of the axiom of choice. The deduction version of this theorem is stoweid 41758: often times it will be better to use stoweid 41758 in other proofs (but this version is probably easier to be read and understood). (Contributed by Glauco Siliprandi, 20-Apr-2017.) |
Ref | Expression |
---|---|
stowei.1 | ⊢ 𝐾 = (topGen‘ran (,)) |
stowei.2 | ⊢ 𝐽 ∈ Comp |
stowei.3 | ⊢ 𝑇 = ∪ 𝐽 |
stowei.4 | ⊢ 𝐶 = (𝐽 Cn 𝐾) |
stowei.5 | ⊢ 𝐴 ⊆ 𝐶 |
stowei.6 | ⊢ ((𝑓 ∈ 𝐴 ∧ 𝑔 ∈ 𝐴) → (𝑡 ∈ 𝑇 ↦ ((𝑓‘𝑡) + (𝑔‘𝑡))) ∈ 𝐴) |
stowei.7 | ⊢ ((𝑓 ∈ 𝐴 ∧ 𝑔 ∈ 𝐴) → (𝑡 ∈ 𝑇 ↦ ((𝑓‘𝑡) · (𝑔‘𝑡))) ∈ 𝐴) |
stowei.8 | ⊢ (𝑥 ∈ ℝ → (𝑡 ∈ 𝑇 ↦ 𝑥) ∈ 𝐴) |
stowei.9 | ⊢ ((𝑟 ∈ 𝑇 ∧ 𝑡 ∈ 𝑇 ∧ 𝑟 ≠ 𝑡) → ∃ℎ ∈ 𝐴 (ℎ‘𝑟) ≠ (ℎ‘𝑡)) |
stowei.10 | ⊢ 𝐹 ∈ 𝐶 |
stowei.11 | ⊢ 𝐸 ∈ ℝ+ |
Ref | Expression |
---|---|
stowei | ⊢ ∃𝑓 ∈ 𝐴 ∀𝑡 ∈ 𝑇 (abs‘((𝑓‘𝑡) − (𝐹‘𝑡))) < 𝐸 |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | nfcv 2929 | . . 3 ⊢ Ⅎ𝑡𝐹 | |
2 | nftru 1767 | . . 3 ⊢ Ⅎ𝑡⊤ | |
3 | stowei.1 | . . 3 ⊢ 𝐾 = (topGen‘ran (,)) | |
4 | stowei.2 | . . . 4 ⊢ 𝐽 ∈ Comp | |
5 | 4 | a1i 11 | . . 3 ⊢ (⊤ → 𝐽 ∈ Comp) |
6 | stowei.3 | . . 3 ⊢ 𝑇 = ∪ 𝐽 | |
7 | stowei.4 | . . 3 ⊢ 𝐶 = (𝐽 Cn 𝐾) | |
8 | stowei.5 | . . . 4 ⊢ 𝐴 ⊆ 𝐶 | |
9 | 8 | a1i 11 | . . 3 ⊢ (⊤ → 𝐴 ⊆ 𝐶) |
10 | stowei.6 | . . . 4 ⊢ ((𝑓 ∈ 𝐴 ∧ 𝑔 ∈ 𝐴) → (𝑡 ∈ 𝑇 ↦ ((𝑓‘𝑡) + (𝑔‘𝑡))) ∈ 𝐴) | |
11 | 10 | 3adant1 1110 | . . 3 ⊢ ((⊤ ∧ 𝑓 ∈ 𝐴 ∧ 𝑔 ∈ 𝐴) → (𝑡 ∈ 𝑇 ↦ ((𝑓‘𝑡) + (𝑔‘𝑡))) ∈ 𝐴) |
12 | stowei.7 | . . . 4 ⊢ ((𝑓 ∈ 𝐴 ∧ 𝑔 ∈ 𝐴) → (𝑡 ∈ 𝑇 ↦ ((𝑓‘𝑡) · (𝑔‘𝑡))) ∈ 𝐴) | |
13 | 12 | 3adant1 1110 | . . 3 ⊢ ((⊤ ∧ 𝑓 ∈ 𝐴 ∧ 𝑔 ∈ 𝐴) → (𝑡 ∈ 𝑇 ↦ ((𝑓‘𝑡) · (𝑔‘𝑡))) ∈ 𝐴) |
14 | stowei.8 | . . . 4 ⊢ (𝑥 ∈ ℝ → (𝑡 ∈ 𝑇 ↦ 𝑥) ∈ 𝐴) | |
15 | 14 | adantl 474 | . . 3 ⊢ ((⊤ ∧ 𝑥 ∈ ℝ) → (𝑡 ∈ 𝑇 ↦ 𝑥) ∈ 𝐴) |
16 | stowei.9 | . . . 4 ⊢ ((𝑟 ∈ 𝑇 ∧ 𝑡 ∈ 𝑇 ∧ 𝑟 ≠ 𝑡) → ∃ℎ ∈ 𝐴 (ℎ‘𝑟) ≠ (ℎ‘𝑡)) | |
17 | 16 | adantl 474 | . . 3 ⊢ ((⊤ ∧ (𝑟 ∈ 𝑇 ∧ 𝑡 ∈ 𝑇 ∧ 𝑟 ≠ 𝑡)) → ∃ℎ ∈ 𝐴 (ℎ‘𝑟) ≠ (ℎ‘𝑡)) |
18 | stowei.10 | . . . 4 ⊢ 𝐹 ∈ 𝐶 | |
19 | 18 | a1i 11 | . . 3 ⊢ (⊤ → 𝐹 ∈ 𝐶) |
20 | stowei.11 | . . . 4 ⊢ 𝐸 ∈ ℝ+ | |
21 | 20 | a1i 11 | . . 3 ⊢ (⊤ → 𝐸 ∈ ℝ+) |
22 | 1, 2, 3, 5, 6, 7, 9, 11, 13, 15, 17, 19, 21 | stoweid 41758 | . 2 ⊢ (⊤ → ∃𝑓 ∈ 𝐴 ∀𝑡 ∈ 𝑇 (abs‘((𝑓‘𝑡) − (𝐹‘𝑡))) < 𝐸) |
23 | 22 | mptru 1514 | 1 ⊢ ∃𝑓 ∈ 𝐴 ∀𝑡 ∈ 𝑇 (abs‘((𝑓‘𝑡) − (𝐹‘𝑡))) < 𝐸 |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ∧ wa 387 ∧ w3a 1068 = wceq 1507 ⊤wtru 1508 ∈ wcel 2048 ≠ wne 2964 ∀wral 3085 ∃wrex 3086 ⊆ wss 3828 ∪ cuni 4710 class class class wbr 4927 ↦ cmpt 5006 ran crn 5405 ‘cfv 6186 (class class class)co 6974 ℝcr 10330 + caddc 10334 · cmul 10336 < clt 10470 − cmin 10666 ℝ+crp 12201 (,)cioo 12551 abscabs 14448 topGenctg 16561 Cn ccn 21530 Compccmp 21692 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1758 ax-4 1772 ax-5 1869 ax-6 1928 ax-7 1964 ax-8 2050 ax-9 2057 ax-10 2077 ax-11 2091 ax-12 2104 ax-13 2299 ax-ext 2747 ax-rep 5047 ax-sep 5058 ax-nul 5065 ax-pow 5117 ax-pr 5184 ax-un 7277 ax-inf2 8894 ax-cnex 10387 ax-resscn 10388 ax-1cn 10389 ax-icn 10390 ax-addcl 10391 ax-addrcl 10392 ax-mulcl 10393 ax-mulrcl 10394 ax-mulcom 10395 ax-addass 10396 ax-mulass 10397 ax-distr 10398 ax-i2m1 10399 ax-1ne0 10400 ax-1rid 10401 ax-rnegex 10402 ax-rrecex 10403 ax-cnre 10404 ax-pre-lttri 10405 ax-pre-lttrn 10406 ax-pre-ltadd 10407 ax-pre-mulgt0 10408 ax-pre-sup 10409 ax-addf 10410 ax-mulf 10411 |
This theorem depends on definitions: df-bi 199 df-an 388 df-or 834 df-3or 1069 df-3an 1070 df-tru 1510 df-fal 1520 df-ex 1743 df-nf 1747 df-sb 2014 df-mo 2544 df-eu 2580 df-clab 2756 df-cleq 2768 df-clel 2843 df-nfc 2915 df-ne 2965 df-nel 3071 df-ral 3090 df-rex 3091 df-reu 3092 df-rmo 3093 df-rab 3094 df-v 3414 df-sbc 3681 df-csb 3786 df-dif 3831 df-un 3833 df-in 3835 df-ss 3842 df-pss 3844 df-nul 4178 df-if 4349 df-pw 4422 df-sn 4440 df-pr 4442 df-tp 4444 df-op 4446 df-uni 4711 df-int 4748 df-iun 4792 df-iin 4793 df-br 4928 df-opab 4990 df-mpt 5007 df-tr 5029 df-id 5309 df-eprel 5314 df-po 5323 df-so 5324 df-fr 5363 df-se 5364 df-we 5365 df-xp 5410 df-rel 5411 df-cnv 5412 df-co 5413 df-dm 5414 df-rn 5415 df-res 5416 df-ima 5417 df-pred 5984 df-ord 6030 df-on 6031 df-lim 6032 df-suc 6033 df-iota 6150 df-fun 6188 df-fn 6189 df-f 6190 df-f1 6191 df-fo 6192 df-f1o 6193 df-fv 6194 df-isom 6195 df-riota 6935 df-ov 6977 df-oprab 6978 df-mpo 6979 df-of 7225 df-om 7395 df-1st 7498 df-2nd 7499 df-supp 7631 df-wrecs 7747 df-recs 7809 df-rdg 7847 df-1o 7901 df-2o 7902 df-oadd 7905 df-er 8085 df-map 8204 df-pm 8205 df-ixp 8256 df-en 8303 df-dom 8304 df-sdom 8305 df-fin 8306 df-fsupp 8625 df-fi 8666 df-sup 8697 df-inf 8698 df-oi 8765 df-card 9158 df-cda 9384 df-pnf 10472 df-mnf 10473 df-xr 10474 df-ltxr 10475 df-le 10476 df-sub 10668 df-neg 10669 df-div 11095 df-nn 11436 df-2 11500 df-3 11501 df-4 11502 df-5 11503 df-6 11504 df-7 11505 df-8 11506 df-9 11507 df-n0 11705 df-z 11791 df-dec 11909 df-uz 12056 df-q 12160 df-rp 12202 df-xneg 12321 df-xadd 12322 df-xmul 12323 df-ioo 12555 df-ioc 12556 df-ico 12557 df-icc 12558 df-fz 12706 df-fzo 12847 df-fl 12974 df-seq 13182 df-exp 13242 df-hash 13503 df-cj 14313 df-re 14314 df-im 14315 df-sqrt 14449 df-abs 14450 df-clim 14700 df-rlim 14701 df-sum 14898 df-struct 16335 df-ndx 16336 df-slot 16337 df-base 16339 df-sets 16340 df-ress 16341 df-plusg 16428 df-mulr 16429 df-starv 16430 df-sca 16431 df-vsca 16432 df-ip 16433 df-tset 16434 df-ple 16435 df-ds 16437 df-unif 16438 df-hom 16439 df-cco 16440 df-rest 16546 df-topn 16547 df-0g 16565 df-gsum 16566 df-topgen 16567 df-pt 16568 df-prds 16571 df-xrs 16625 df-qtop 16630 df-imas 16631 df-xps 16633 df-mre 16709 df-mrc 16710 df-acs 16712 df-mgm 17704 df-sgrp 17746 df-mnd 17757 df-submnd 17798 df-mulg 18006 df-cntz 18212 df-cmn 18662 df-psmet 20233 df-xmet 20234 df-met 20235 df-bl 20236 df-mopn 20237 df-cnfld 20242 df-top 21200 df-topon 21217 df-topsp 21239 df-bases 21252 df-cld 21325 df-cn 21533 df-cnp 21534 df-cmp 21693 df-tx 21868 df-hmeo 22061 df-xms 22627 df-ms 22628 df-tms 22629 |
This theorem is referenced by: (None) |
Copyright terms: Public domain | W3C validator |