SURE: Shizuoka University REpository http://ir.lib.shizuoka.ac.jp/ Title Author(s) Citation Issue Date URL Version Generalized Sierpinski Functions and Fragmentable Compact Spaces Matsuda, Minoru Reports of Faculty of Science, Shizuoka University. 35, p. 7-15 2001-02-28 http://dx.doi.org/10.14945/00000872 publisher Rights This document is downloaded at: 2015-01-31T17:48:27Z Reports of the Faculty of Science, Shizuoka University, Vol.35, pp.7-15 (2001) Ori,ginal Paper Generalized, Sierpinski Functions and Fragmentable Compact Spaees Minoru MRrsuolt Defuartment of Mathemntics, Faculty of Science, Shi,zuoka Uni,uersi,ty, Ohya, Shizuoka 422-8529 (Receiaed Nouember 29, 2000) Abstract: We present functions named generalized Sierpinski function, each of which can be regarded as a generalization of the so-called Sierpinski function. Making use of these functions, we make a direct study of two types of fragmentable compact spaces in the measure-theoretic aspect. 2000 Mathematics Subject Classification: 46822, 46807. Key words and phrases: generalized Sierpinski function, H-fragmentable compact space, weak H -fragmentable compact space 1. Introduction Let X be a real Banach space and X* its topological dual space. In our recent paper [7], for a bounded subset A of. X and a weak*-compact subset K of. X*, we have defined two notions on sets K called A-Pettis sets and A-Radon-Nikodym sets (slight generalizations of Pettis sets and norm-fragmented sets, respectively), and we have made a simultaneous and unified study of such sets by constructing K-valued functions associated with non-A-Pettis sets or non-1.-Radon-Nikodym sets and making use of them effectively. In this paper, we are going to investigate such type of notions in a more general setting by following the same ideas as in [7] (refer also to [S] and [6]). Now, our setting is as follows. Let Y be a compact Hausdorff space, C(Y) the Banach space of all real-valued continuous functions on Y, and let us give our attention to the following two types of tE-mail: smmmatu @ ipc.shizuoka.ac jp Minoru Mersuna fragmentability of Y associated with a bounded subset H of. C(Y).The notion of fragmentability has appeared in [3]. Definition L (H-fragmentability of Y\. Let e fragmentable if for every nonempty closed subset. M of I there exists an open subset G of Y suchthat M n G+aand diam, (M n G) (- sup{VU) - fbdli !r, lz e. M n G, f e H\) ( e, and IZ is said to be H-fragrnentable if IZ is (H, e)-fragmentable for every e)0. Note that this is correspondent to the notion of .F/-Radon-Nikodym sets in dual Banach spaces, and (H, e)-fragmentability has been used in l2l to analyze Radon-Nikodym compacta. Definition 2 (Weak H -fragmentability of. Y). Let e ) 0. We say that Y is weak (H, e)-fragrnentable if for every nonempty closed subset M of. Y and every f e Ho (: the closure of. H with respect to the pointwise convergence topology on Y) there exists an open subset G of Y such that M i G + fr and OVIM n G) (-- sup {Vbil - fU,)l : y,, lz€MnG)) e)-fragmentable for every e) 0. Note that this is equivalent to the notion of weak precompactness of. H (That is, .F/ does not contain an /r sequence. For further details of weak precompactness subsets I/ of C(IZ), see Theorem 7.3.1 in [8]) ana this is coffespondent to the notion of .F/-Pettis sets in dual Banach spaces. Further, H -fragmentability of Y naturally implies weak H -fragmentability of. Y . Our study in this paper is a direct and simultaneous consideration of measure-theoretic characterizations of these notions with the aid of Y-valued functions on .I (- [0,1]) constructed in the case where Iz is a non-H -fragmentable space or a non-weak f/fragmentable space. That is, we wish to give some more characterizations of such sets, which are completely analogous to the results in [7]. The paper is orgaruzed as follows. In $2, we show the existence of generalized Sierpinski functions under some general conditions by the same argument as in [a]. Each of them can be regarded as a generalization of the well-known function, so"called Sierpinski function. Making use of this result, in 53, we can present basic generalized Sierpinski functions which are very useful in analyzing directly H -fragmentable compact spaces and weak H-fragmentable compact spaes. In view of this consideration, in $4, we can give some measure-theoretic characterizations of these spaces, from which we can recognize their similarity and difference in the measure-theoretic aspect. Thus this paper may be regarded as a complete analogue of [7], although it is written under a more general setting. In other words, this also indicates that our method introducing general- Generalized Sierpinski Functions and Fragmentable Compact Spaces ized Sierpinski functions makes it possible to analyze such general spaces in a direct mamer lby the complete same argument as in[7]),which is an appealing point of our paper. 2。 Generalized Sierpinski functions Let us begin with the following: Definition 3(Generalized Sierpinski functions).Let T and S be compact Hausdorff spaces,力 be a continuous surieCtiOn fron1 7¬ to S,and νbe a lRadon probability measure on S.Then a function λ:S→ r is said to be a`″ %ι ,ヮ ′ ″′ グS′ι 脇〔 ψ;ルπσ πθ%associated ψ焼 ν)if the fol10wing three conditions are satisfied. (1)The function力 is a〃 (S)‐ ン (T)measurable ftlnction such that力 (ν )(the image measure of νby tt is a Radon probability measure on T,where〃 (S)(resp.´ (r)) ・algebra of S(resp.T). denotes the Borel σ with a pair(力 , (2)力 (λ (ν ))=ν 。 (3)/(力 (力 (′ )))=/(′ ),力 (ν R′ %α ′ 滋 )‐ aoe.for each/∈ C(r)。 1.If r is a compact metrizable space,the condition(3)in Definition 3 may be replaced by a.e.on T, since C(r)is separable. (彙 )λ (力 (′ ))=′ ,力 (ν )・ Here,we wish to show the existence of generalized Sierpinski functions associated with such a pair(力 , ν Before stating it, let us see the Sierpinski function in our )。 framewOrko Let r be the cantor space{0,1}Ⅳ ,S the unit interval f,and λthe Lebesgue measure on fo Let%≧ :l and let rpz denote the%th]Rademacher function on r defined by 場(s)=Σ k=1 for every s∈ f,where r(力 ,グ 1ル (-1)力 0,o(S) 1)/22,グ /2つ if%≧ 1,1≦ ′ ≦2π -l and f(π ,2つ )=[(グ ー = [(22-1)/211]if%≧ 0.Define力 :{0,1}Ⅳ → f by力 ({場 }た 1)=Σ 鷹1場 /2π for every′ = 1∈ {0,1}Ⅳ .Thenヵ is a continuous suriectiOno cOnsider the function(so‐ called {為 }″ ≧ Sierpinski functiOnl λ:r→ {o,1}Ⅳ defined by 力 (s)=(0-場 (s))/2}π ≧ 1 for every s ∈ f.Then we get that (1)The function λis a″ (r)・ ´({o,1}り measurable fШ lction such that λ (λ )iS a nOrmalized Haar measure on{0,1}Ⅳ (2)力 (λ (λ ))):= λ,and , Minom MATSUDA (3)λ (力 (′ ))=′ ,λ (λ a.eo on{0,1}性 )‐ Hence the Sierpirlski function can be regarded as a generalized Sierpinski function associated with this pair(た ,λ ),Since(0,1}Ⅳ is a cOmpact metrizable space. Now,let us prove the follo宙 ng: ι ′rα%グ sみ ι ttCσ ′ `η 比豚あグ 軍脇θ 6,力 ι ′ 」 ′αωπ″%%ο 雰 協″ b%/ra%r"Sα %″ νι ′αRα あ%夕 知滋み 妙 `ガ %ι %″ 0%Sa乙 夕 ″ %ヵ物π″ぉおα♂7%ι πルι グS′ι %ε J笏 %λ 6sο 磁 ″ グ ′ λαρα ψれ壺グ ルι "′ “ (力 ,ソ Theore】 ml(Existence of generalized Sierpinski fmctions).ι )。 Praぼ The ar_ent developed here is almost the same as in[4](or[5]).So we give an outline of the proof for the sake of ilnportance.Let(S,Σ ν ,ν )(resp.(T,Σ μ ,μ ))be the completion of(S,多 (S),ν )(resp.(T,多 (r),μ )).Then,by virtue of the well・ known result (1,2,5)in[8]or PropOSition B。 l in[1]),we have a Radon probability measure μ on T such that力 し)=ν and Zl(r,Σ μ l(S,Σ ν ,ν )}.Define a linear ,μ )={g。 力:θ ∈ ι operator y:Ll(s,Σ ν ,ν )→ Zl(r,Σ μ ,μ )by 7(g)=g。 力for every g∈ ιl(S,Σ ν ,ν ).Then aoe.on r for every the operator 7 is a suriectiVe isometry such that y中 び)(力 (′ ))=/(′ )μ ‐ (cf。 0/2)=7*“ )07*α )(in ,μ )and 7*“ /∈ L(T,Σ μ L(S,Σ ν ,ν ))forバ ,/2∈ JL(T,Σ μ , μ Here 7・ denotes the dual operator of 7. )。 Let′ be a lifting on L (S,Σ ν ,ν ).For each s(≡ S,the bounded linear functional Ls on c(r)defined byム び)=′ (7*び ))(S)fOr every/∈ C(r)is multiplicat市 e and so,we have a function λ:S→ r such that/(λ (S))=′ (7*び ))(S)fOr every/∈ C(r)and every s∈ S.Hence we have that′ び。 劾 =/。 λfOr every/∈ C(r).Thus,by宙 rtue of the lifting λis a〃 (S)Ⅲ 〃(r)measurable function such that λ (ν )iS Radono So the condition(1)is satisfied.Moreover,/(λ (S))=7*び )(s)ν ‐ aoe.on s for evelγ /∈ C(r). theory,we get that a.e.On r for every し)=ν and 7中 び)(力 ))=/(′ )μ ‐ a.e.on r for every/∈ C(r).Hence we have )))=/(′ )μ ‐ Combining this with the result that力 /∈ c(r),we have that/(λ (力 (′ (′ that !)rutoo1''1 -_ l)rwao))dp(t) f,ru'llankxs) Ifl,lant xtl - [,rus))du(s) for every/∈ C(r).Thus we get that μ =π ν ),and so the conditions(2)and(3)are satisfied.Hence the proof is completed. Rι %α ,脅 2.Since it holds that/(λ that for every E∈ 〃 (S) (力 (′ a.e.On r for every/∈ Crr),we have )))=ノ (′ )μ ¨ Generalized Sierpinski Functions and Fragmentable Compact Spaces 11に /(′ )み (′ )=11に /(λ =ル (力 (′ )))″ (′ ) (λ (S))激 し)(S)=ル (λ (s))ん (S) for every/∈ C(r). Now,for the convenience of readers,let us indicate here the typical case where the existence of generalized Sierpinski functions can be guaranteed. Let y be a compact Hausdorff space and suppose that there exists a system(7(η ′ ): %=0,1,¨ 。;′ =0,… ,2″ -1}of nOnempty dosed subsets of y such that y(%+1,2グ ) 7(aグ )α %グ 7(%+1,2′ )∩ 7(%+1,2′ +1)=O for%=0,1,… and ′=0,… ,2″ -1.Then,letting 4π =∪ {7(%,2グ +1):0≦ ′≦ 22 1-1}and鳥 = ∪{7(%,2′ ):0≦ グ≦22 1-1},T=∩ 鷹1(4π ∪a)is a nonempty compact subset of y.Define ψ:T→ {0,1}Ⅳ by ψ )={為 }た l where均 =l if′ ∈ 4″ and物 =O if′ ∈ 鳥.Then ψis a∞ ntinuous suriectiOn.Further,consider a functionノ :{0,1}″ →r deined byノ 0)=Σ 鷹 1場ノ22,where″ ={為 }″ ≧l∈ (0,1}Ⅳ .Thenノ iS a cOntinuous suriectiOn.Let ∪ 7(%+1,2グ +1)⊂ (′ 力=ノ 。 ψ :r→ f.Then we have a generalized Sierpinski function with this pair(力 ,λ (a)ノ け 0)=λ )。 λ(:r→ r)associated So,letting μ =λ (λ ),we have that , 0)1“ ′ .に D力 )み し)=1/(as))み ●) for every E∈ 〃(r)and every/∈ C(y)。 These are derived from Remark 2 and the fact that μ is regarded as a lRadon probability measure(on y)supported by T。 3.Basic generalized Sierpinski functions associated with non‐ 』 7‐ fragmentable spaces or non― weak J‐ fragmentable spaces ln what fonows,an notations and terminology,unless otherwise stated,are as in[7]. Let y be a compact Hausdorff space.If/:J→ y is a〃 (I)¨ 〃(y)measШ rable ftmctiOn,we obtain a bounded linear Operator 2レ :C(y)→ Zl given by lみ (の =σ O/fOr every σ∈ C(7).For such a function/,we get a system{22Tナ (ル レ,JD:%=0,1,… ;グ = 0,・ ",2″ -1},which is a tree in C(y)ホ 。 In the following,this is called a tree associated With/。 Now, let us present a fundamental result which makes it possible to analyze ″‐ frattentable spaces and weak ″ ‐ frattentable spaces in a direct and simultaneous manner fron■ the measure‐ theoretic view‐ point.This is a complete analogue of Proposi‐ tion 5 in[7]. Theorem 2。 Lι ′yみ ′αωttcσ ′麟 α Oグ 勁 “ α %グ ″ み ′αι ο %%滋 グsπおι ′o/C(y). L/1inoru MATSUDA ι 勿′yた %ο ′二 ι πttι /aJJa"グ ばs滋 ″zι πた(Pl α %″ fQl λ ι ο a 均%召 zι πttι ル ・ηわ “ q お′α夕asグ″υ ″ αsys″ π {/2,J:%=0,1,… ;′ =0,… ,2″ -1}勿 ′π%%ι ′ lPl ηttπ ″ 〃α %″ αsys″ %{7(%,グ ):%=0,1,… ;グ =0,… ,22-1}グ %ο %ι %″ 夕 彰グS%ゐ ο お `わ yS%磁 ′ 滋′ グ (a)7(%+1,2グ )∪ 7(%+1,2グ +1)⊂ 7(%,′ ), (b)%∈ 7(%+1,2′ )α %″ υ∈ 7(%+1,2グ +1)シ ψ夕 ん (%)一 ん,J(υ )≧ c/a″ %=0,1,… α%グ グ=0,・ “ ,2″ -1. 厖 グS′ι lQl tt υ 鶴カ グル%`励 %力 :f→ yw勧 グ fPl,ω ιttυ ια多%ι πル′ ψグ η ttθ (1)S〃ψasa ,ゴ "グ 商″ S. 力JJa"グ 響 夕%″ 夕 θassOσ 勿″″ ′ あ力なαπJ手 (c/2)け π夕 (a)動 ι″′ . "グ (D Jft潔 力)(s)一 二び。 ヵ)(S】 )み (s)≧ c/2 し +1び ° 当 日 foreueryn2L. (c) The set {f"kif e H} X not equimeasurable in I^. (D Suppose tlat Y is not ueak H-fragmentable. Then the following statements @ and (s) hold. (N There exist a positiue number e, a seq?,cence {f"I or,, in H and a system {W(n, i) : n 0, 1, .." ; i : 0, ... , 2n - L| of nonempfii closed subsets of Y such thnt (a) W(ntL,zi) U W(n*I,zi+L) c W(n, i), (b) u e, w(n*r,Zi) and u € w (n*L,zi+r) imbly .f"*r(u) - f"*r(a) 2 e for n = 0, L, ...andi:0,...,2n-L. (S) In uiew of (N, we laae a generalized Si,er?inski function h: I - Y satisfuW the fo llowi.ng prop erti,es. (a) The tree associated with h is an H-separated (e/2)-tree. O sup‖ ノ∈″ 。 島。 劾―島び 1≧ の ‖ 習│ル +1び foreueryn2L. (c) The set { f "h: f e Hl i^s (as》 %③ 況01≧ c/2 not relatiuely norrn compact in Lr. Proof. Since the proof can be given by the complete same argument as that of Proposition 5 in [7], it is omitted. 4. Chara ctefizations of fragmentable compact spaces Making use of results in preceding sections, we are going to give some measuretheoretic characterizations of H -fragmentable compact spaces and weak H fragmentable compact spaces. Concerning H -fragmentable compact spaces, we have: Generalized Sierpinski Functions and Fragmentable Compact Spaces L3 αωの α ′肋 箔あ″rs″ α σ %グ 〃 bι αめ %%滋 ″s%ゐο ο ′グ C(y). “ yα 動ι π′ 滋 /aJJa"′ 響 S滋 滋 ι %お α 0%′ %グ ″ ″ι υ α ″%洗 め α μグ ル (a)yな 月7姥g%ι π滋み υ ι (b)Faγ ι ιassOθ 滋″グ紗′ ′ み/た η 〃(r)_〃 (y)協 ι %π bル ル%ι 励%/:J→ Кttθ ″ι “ %0′ α %μ δ″θ ι 。 υ ι 厖ル″ (C)乃 ″θ %θ 滅,%/」 J→ Z″ 力 ο JJs′ 滋′ η 〃(r)‐ 〃(y)2ι ω%π み Theorem 3.ι ι ′y bι . 縫ilプ k:当 1島 (o)」 +1(gO/)(S)一 島 (σ O/)(S)D裁 (s)}=0。 勁″ι υ ι ルル%σ 励%/:f→ Кttι sι ′{θ O/:J∈ ″}た η 〃(f)‐ 〃(y)2″ s%π み ι σ%′%ι %ηb厖 ′ %L. `雰 助 グ The Same ar_ent as in[6]and[7]easily deduces that O)⇒ (C)→ (b). (b)⇒ (a).This part is crucial and it follows from Theorem 2. So we have only to show that(a)⇒ To this end,take a〃 (r)‐ 〃(y)measurable function/:f → И Then,by virtue of the lifting theory,we have a〃 (f)‐ ′(y) 。 measurable function力 :f→ y such that λ (λ )(=μ )is Radon and{gO/:g∈ 〃}=(θ λ:g∈ 〃}in Lo By the property of Radon mё asures on y and″ ‐ fraglllentability of (d)。 y,we easily get that for every positive nurnber c and every element 4 of Z(y)with μ(4)>0,there exists an element 3 of〃 (Y)with μ(3)>O and B⊂ z4such that supg∈ 〃 0(dB)<c.Hence,the well‐ knowFl eXhaustion ar_ent deduces that for every positive nurnber c,there exists a disiOint sequence{E″ }″ ≧ 1⊂ 〃(γ ),all of positive measure, μ¨ )=O and supθ c〃 0(σ lβ″ μ(yヽ ∪鷹1拓場 )<c for every%≧ 1.Thus,taking EL= -1(a)for every π≧1,for every positive number c,we have a disioint Sequence{島 ヵ }π ≧ ⊂ A,a1l of positive卜 measure,such that λ(I\ ∪鷹12)=O and supθ ∈ ″0(′ 。 冽E″ )< such that 1 c for every%≧ 1.Therefore,the same ar_ent as in the proof of Proposition 3 in[6] deduces that{g。 力:σ ∈ ″}is equimeasurable in L,whence we complete the proof. Concerning weak″ ‐ fragmentable compact spaces,we have: Theorem 4.ι ι ′yみ ιασ ο ttQ`′ 肋 郷あグ ψα ″α %グ 〃 ι ′αι ο %π 滋″s%決グ a/C(y). αι O%′ yα %グ 〃 α %θ σ %グ υ αル%洗 η ι ι 滋 」 ¢ %″ み (a)yな ル 躊ル婆″ ι υ ι (b)Д 9″ ι 6%π み厖ル%σ 励%/:f→ К ttθ ″ιιassο ″グ ′ λ/た η :〃 (r)_′ (y)協 ο "グ `滋 %0′ α %flsィ滋π″グ δttc. υ ι 6%zb厖 ル%σ 滅)%/:f→ К ″λο (C)乃 ″θ JJs′ 滋′ η 〃(f)‐ 〃(y)協 ι aゎ ι %滋 θ/aJJa"グ %ば s滋 ″πι %た . 2+1(gO/)一 EXgO/)‖ 1〕 縫I{:』 ‖ =磐 {:当 1/gび (S))場 (s)激 (s】 }=0. %/:f→ Кttι sι ′{gO/:′ ∈ 〃}お ぅ ι (d)nフ ″ι 6%π み 厖ル%σ 励 η 〃(f)‐ 〃(y)協 ι π滋励 ι 物 σ Ottσ ′物 ιl. 夕 πο″ Minoru MATSUDA Praグ The same arttent as in[5]and[7]easily deduces that(d)⇒ (C)⇒ (b)。 (b)⇒ (a).This part is crucial and it follows from Theorem 2. So we have only to see that(a)=⇒ ld),which follows fronl the bounded convergence theorelTl,since(a)is equivalent to that ttr is weakly precompact。 Rι ″協″ {ら :ノ ∈ a For everyノ ∈ y,letら denote the umt point measure atノ and let δ(y)= y}.Then δ(y)is a weak*_compact subset of C(7)申 and wei― ediately get that y is″ _fragmentable(resp.weak〃 ・fra≦要lentable)if and only if δ(y)is an ″‐ Radon‐ Nikodtt set(resp.″ ‐ Pettis set)。 So we knOw that our Theorems 3 and 4 can be derived easily from Theorems l and 2(Characterization Theorems of″ ¨ Radon¨ Pettis sets)in[7],respectively.Consequently,as stated in§ Nikodtt sets and″ ‐ 1,the ,τ ε ′way to ″′ ‐ 〃‐ ″ fraglllentable compact spaces and weak only thing to be ёmphsized in this paper may be that we can present a analyze general spaces, such as frattentable compact spaces,by introducing gttπ ι π」 ″aa Sierpinski functions. 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Generalized Sierpinski Functions and Frattentable Compact Spaces 15 -般 化 され た シ ェル ピンス キ ー 関 数 と フ ラ グ メ ン ト可 能 な コンパ ク ト空 間 松 田 稔 静岡大学理学部数学教室 〒422-8529静 岡市大谷836 シェルピンスキー関数の拡張 と考えられる一般化されたシェルピンスキー関数を新たに定 義 し,そ れを構成する.こ の関数を利用することにより,二 つの種類のフラグメン ト可能な コンパクト空間の測度論的側面での,並 行的,直 接的考察を行なう .
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