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Theorem stowei 38957
 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 38956: often times it will be better to use stoweid 38956 in other proofs (but this version is probably easier to be read and understood). (Contributed by Glauco Siliprandi, 20-Apr-2017.)
Hypotheses
Ref Expression
stowei.1 𝐾 = (topGen‘ran (,))
stowei.2 𝐽 ∈ Comp
stowei.3 𝑇 = 𝐽
stowei.4 𝐶 = (𝐽 Cn 𝐾)
stowei.5 𝐴𝐶
stowei.6 ((𝑓𝐴𝑔𝐴) → (𝑡𝑇 ↦ ((𝑓𝑡) + (𝑔𝑡))) ∈ 𝐴)
stowei.7 ((𝑓𝐴𝑔𝐴) → (𝑡𝑇 ↦ ((𝑓𝑡) · (𝑔𝑡))) ∈ 𝐴)
stowei.8 (𝑥 ∈ ℝ → (𝑡𝑇𝑥) ∈ 𝐴)
stowei.9 ((𝑟𝑇𝑡𝑇𝑟𝑡) → ∃𝐴 (𝑟) ≠ (𝑡))
stowei.10 𝐹𝐶
stowei.11 𝐸 ∈ ℝ+
Assertion
Ref Expression
stowei 𝑓𝐴𝑡𝑇 (abs‘((𝑓𝑡) − (𝐹𝑡))) < 𝐸
Distinct variable groups:   𝑓,𝑔,𝑡,𝐴   𝑓,,𝑟,𝑥,𝑡,𝐴   𝑓,𝐸,𝑔,𝑡   𝑓,𝐹,𝑔,𝑡   𝑓,𝐽,𝑟,𝑡   𝑇,𝑓,𝑔,𝑡   ,𝐸,𝑟,𝑥   ,𝐹,𝑟,𝑥   𝑇,,𝑟,𝑥   𝑡,𝐾
Allowed substitution hints:   𝐶(𝑥,𝑡,𝑓,𝑔,,𝑟)   𝐽(𝑥,𝑔,)   𝐾(𝑥,𝑓,𝑔,,𝑟)

Proof of Theorem stowei
StepHypRef Expression
1 nfcv 2751 . . 3 𝑡𝐹
2 nftru 1721 . . 3 𝑡
3 stowei.1 . . 3 𝐾 = (topGen‘ran (,))
4 stowei.2 . . . 4 𝐽 ∈ Comp
54a1i 11 . . 3 (⊤ → 𝐽 ∈ Comp)
6 stowei.3 . . 3 𝑇 = 𝐽
7 stowei.4 . . 3 𝐶 = (𝐽 Cn 𝐾)
8 stowei.5 . . . 4 𝐴𝐶
98a1i 11 . . 3 (⊤ → 𝐴𝐶)
10 stowei.6 . . . 4 ((𝑓𝐴𝑔𝐴) → (𝑡𝑇 ↦ ((𝑓𝑡) + (𝑔𝑡))) ∈ 𝐴)
11103adant1 1072 . . 3 ((⊤ ∧ 𝑓𝐴𝑔𝐴) → (𝑡𝑇 ↦ ((𝑓𝑡) + (𝑔𝑡))) ∈ 𝐴)
12 stowei.7 . . . 4 ((𝑓𝐴𝑔𝐴) → (𝑡𝑇 ↦ ((𝑓𝑡) · (𝑔𝑡))) ∈ 𝐴)
13123adant1 1072 . . 3 ((⊤ ∧ 𝑓𝐴𝑔𝐴) → (𝑡𝑇 ↦ ((𝑓𝑡) · (𝑔𝑡))) ∈ 𝐴)
14 stowei.8 . . . 4 (𝑥 ∈ ℝ → (𝑡𝑇𝑥) ∈ 𝐴)
1514adantl 481 . . 3 ((⊤ ∧ 𝑥 ∈ ℝ) → (𝑡𝑇𝑥) ∈ 𝐴)
16 stowei.9 . . . 4 ((𝑟𝑇𝑡𝑇𝑟𝑡) → ∃𝐴 (𝑟) ≠ (𝑡))
1716adantl 481 . . 3 ((⊤ ∧ (𝑟𝑇𝑡𝑇𝑟𝑡)) → ∃𝐴 (𝑟) ≠ (𝑡))
18 stowei.10 . . . 4 𝐹𝐶
1918a1i 11 . . 3 (⊤ → 𝐹𝐶)
20 stowei.11 . . . 4 𝐸 ∈ ℝ+
2120a1i 11 . . 3 (⊤ → 𝐸 ∈ ℝ+)
221, 2, 3, 5, 6, 7, 9, 11, 13, 15, 17, 19, 21stoweid 38956 . 2 (⊤ → ∃𝑓𝐴𝑡𝑇 (abs‘((𝑓𝑡) − (𝐹𝑡))) < 𝐸)
2322trud 1484 1 𝑓𝐴𝑡𝑇 (abs‘((𝑓𝑡) − (𝐹𝑡))) < 𝐸
 Colors of variables: wff setvar class Syntax hints:   → wi 4   ∧ wa 383   ∧ w3a 1031   = wceq 1475  ⊤wtru 1476   ∈ wcel 1977   ≠ wne 2780  ∀wral 2896  ∃wrex 2897   ⊆ wss 3540  ∪ cuni 4372   class class class wbr 4583   ↦ cmpt 4643  ran crn 5039  ‘cfv 5804  (class class class)co 6549  ℝcr 9814   + caddc 9818   · cmul 9820   < clt 9953   − cmin 10145  ℝ+crp 11708  (,)cioo 12046  abscabs 13822  topGenctg 15921   Cn ccn 20838  Compccmp 20999 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1713  ax-4 1728  ax-5 1827  ax-6 1875  ax-7 1922  ax-8 1979  ax-9 1986  ax-10 2006  ax-11 2021  ax-12 2034  ax-13 2234  ax-ext 2590  ax-rep 4699  ax-sep 4709  ax-nul 4717  ax-pow 4769  ax-pr 4833  ax-un 6847  ax-inf2 8421  ax-cnex 9871  ax-resscn 9872  ax-1cn 9873  ax-icn 9874  ax-addcl 9875  ax-addrcl 9876  ax-mulcl 9877  ax-mulrcl 9878  ax-mulcom 9879  ax-addass 9880  ax-mulass 9881  ax-distr 9882  ax-i2m1 9883  ax-1ne0 9884  ax-1rid 9885  ax-rnegex 9886  ax-rrecex 9887  ax-cnre 9888  ax-pre-lttri 9889  ax-pre-lttrn 9890  ax-pre-ltadd 9891  ax-pre-mulgt0 9892  ax-pre-sup 9893  ax-addf 9894  ax-mulf 9895 This theorem depends on definitions:  df-bi 196  df-or 384  df-an 385  df-3or 1032  df-3an 1033  df-tru 1478  df-fal 1481  df-ex 1696  df-nf 1701  df-sb 1868  df-eu 2462  df-mo 2463  df-clab 2597  df-cleq 2603  df-clel 2606  df-nfc 2740  df-ne 2782  df-nel 2783  df-ral 2901  df-rex 2902  df-reu 2903  df-rmo 2904  df-rab 2905  df-v 3175  df-sbc 3403  df-csb 3500  df-dif 3543  df-un 3545  df-in 3547  df-ss 3554  df-pss 3556  df-nul 3875  df-if 4037  df-pw 4110  df-sn 4126  df-pr 4128  df-tp 4130  df-op 4132  df-uni 4373  df-int 4411  df-iun 4457  df-iin 4458  df-br 4584  df-opab 4644  df-mpt 4645  df-tr 4681  df-eprel 4949  df-id 4953  df-po 4959  df-so 4960  df-fr 4997  df-se 4998  df-we 4999  df-xp 5044  df-rel 5045  df-cnv 5046  df-co 5047  df-dm 5048  df-rn 5049  df-res 5050  df-ima 5051  df-pred 5597  df-ord 5643  df-on 5644  df-lim 5645  df-suc 5646  df-iota 5768  df-fun 5806  df-fn 5807  df-f 5808  df-f1 5809  df-fo 5810  df-f1o 5811  df-fv 5812  df-isom 5813  df-riota 6511  df-ov 6552  df-oprab 6553  df-mpt2 6554  df-of 6795  df-om 6958  df-1st 7059  df-2nd 7060  df-supp 7183  df-wrecs 7294  df-recs 7355  df-rdg 7393  df-1o 7447  df-2o 7448  df-oadd 7451  df-er 7629  df-map 7746  df-pm 7747  df-ixp 7795  df-en 7842  df-dom 7843  df-sdom 7844  df-fin 7845  df-fsupp 8159  df-fi 8200  df-sup 8231  df-inf 8232  df-oi 8298  df-card 8648  df-cda 8873  df-pnf 9955  df-mnf 9956  df-xr 9957  df-ltxr 9958  df-le 9959  df-sub 10147  df-neg 10148  df-div 10564  df-nn 10898  df-2 10956  df-3 10957  df-4 10958  df-5 10959  df-6 10960  df-7 10961  df-8 10962  df-9 10963  df-n0 11170  df-z 11255  df-dec 11370  df-uz 11564  df-q 11665  df-rp 11709  df-xneg 11822  df-xadd 11823  df-xmul 11824  df-ioo 12050  df-ioc 12051  df-ico 12052  df-icc 12053  df-fz 12198  df-fzo 12335  df-fl 12455  df-seq 12664  df-exp 12723  df-hash 12980  df-cj 13687  df-re 13688  df-im 13689  df-sqrt 13823  df-abs 13824  df-clim 14067  df-rlim 14068  df-sum 14265  df-struct 15697  df-ndx 15698  df-slot 15699  df-base 15700  df-sets 15701  df-ress 15702  df-plusg 15781  df-mulr 15782  df-starv 15783  df-sca 15784  df-vsca 15785  df-ip 15786  df-tset 15787  df-ple 15788  df-ds 15791  df-unif 15792  df-hom 15793  df-cco 15794  df-rest 15906  df-topn 15907  df-0g 15925  df-gsum 15926  df-topgen 15927  df-pt 15928  df-prds 15931  df-xrs 15985  df-qtop 15990  df-imas 15991  df-xps 15993  df-mre 16069  df-mrc 16070  df-acs 16072  df-mgm 17065  df-sgrp 17107  df-mnd 17118  df-submnd 17159  df-mulg 17364  df-cntz 17573  df-cmn 18018  df-psmet 19559  df-xmet 19560  df-met 19561  df-bl 19562  df-mopn 19563  df-cnfld 19568  df-top 20521  df-bases 20522  df-topon 20523  df-topsp 20524  df-cld 20633  df-cn 20841  df-cnp 20842  df-cmp 21000  df-tx 21175  df-hmeo 21368  df-xms 21935  df-ms 21936  df-tms 21937 This theorem is referenced by: (None)
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