TRU Mathematics 15−2 〔1979〕
THE BOCHNER INrEGRAL FOR剛CTIONS WITH VALUES
IN THE UNION OF RANKED VECTOR SPACES
. Yoshiko TAGU〔HI (Received November 16, 1979〕 K.Ku【lugi defined the ranked space of indicatorωo in l954([3],[4D. S.Nakanishi has defined the union of ranked spaces in 1974([6],[8]). The BamaCh space is considered as the ranked space of indicatorωo([7]).[[he union of suCh ranked spaces is called the uni㎝of ranked vector spaces. On the other hand, S.Bodhner defined the integral for the Bana(沮space valued functions in 1933〔[1D. In this note, we define the Bodhner integral fOr fuhctions with values in the union of ranked vector spaces and show so皿e properties of the integral. 1. Preli皿inaries. 1.1. Ranked spaces. A none㎎)ty set E is called the ranked space(of in− dicatorωo) if it is e(luipped with the nonempty families U(ρ)〔ρε E) andひ〔n〕 @ ε N={0,1,2,...}) satisfying the conditions (A) and (a): (A)For everyγ(ρ)ετρ〔P),PεV(ρ). (a〕 For eadh V(ρ〕 ε び(ρ〕 and eadh nε N, there are a nu凪)er mε N and a σ(ρ) εZS(ρ) satisfyillg that n <栩, [ノ〔P)(二 V〔P〕 and 〃〔ρ)εてタ(in). The element of 7フ(P),written γ(ρ〕, is called the preneighborhood of P and that ofび(n),written V(ρ) or 7〔p,n), the preneighborhood of p of rank n. The ranked space E is written 〔E,’び〔P〕,’tタ〔n)) or E simply. 1・a r・nk・d・pace・E…equence・f pren・ighb・rh・・dS{VIPk・nk)}〔k・めi・ called a fundamentaユsequence if the following conditions are satisfied: (1)γ@た・nk)⊃γ鮎ヱ・nk.1〕f・r ea・in k・(2)nk≦nk+1 f・r・a・in k・ ・
〔3)F・rea・in k・there i・ ・n Z…hth・t Z≧k・pZ = pZ+ヱand ・Z<nUl・ A fundamenta1 seq・・nce i・ca11・d th・t・f・・nter p if p瓦一pf・r ・11 k・ Aran](ed space E is called comPlete if, for every f皿(lamental sequence {γIPk’nk〕}・ハ{ViPk・nk)}≠〆・A・equence{pk}i・Ei・ca11・d r−c・nverg・・t・r t°「−c°nve「g・t・P and・w・岨t・P=・−Zi・ pk・if th・・e i・a]imda・e・t・1 seq・− ence{γ@・nk〕}・f・enter・P・ati・fyi・g th・fb11・w血9・・nditi㎝・F・・ea・h k, th・r・i・an i・su・;h th・t pi・ViP・nk)if i≧i・・’ 1・2・ The uniσn of ranked vector spaces. Let E be a vector space and 5556 Y.TAGUCHI、 {E(α);α ε、4}(4 is an index set〕 a family of subspaces of E in the algebraic ・ens・and・mPP・se th・t each E〔・)i・a麺紬印ace岨th・n・m ll ll。 and・th・ following three conditions are satisfied: 〔i) E; ∪{E〔α〕; α εA}. (五) Foτany E〔α〕 and E〔β), there exists an E(Y) sudh that E〔α〕UE(β)⊂ E(Y). (皿)lf E〔・)CE(β)・th・n・f・r・v・ry・P・E(・)・1[pll。−llpllβ・ The vector space E equipped with Z9(p) andてタ〔n) defined by the following way, written 〔E, Z9(p),’U,〔n〕) or E si巫4)1y, is called the union of ranked vector spaces・ For eachαεA, the families of sUbsets of E〔α〕,び(P,α) and Zタ(n,α) .are defined: and V(P, n,α) hood of p of rank n respectively, such that zタ(P〕=∪{び(ρ,α〕;αεA3μ・h that PεE〔α)},ρεE, ’ty (n)=∪{戸び〔n,α);αεA}. The element of万〔ρ) is often written V〔P) and that ofび(n〕, び(P,α) sε〔α) ひ(nsα) s(n,α) s(o,α) v(ρ,α)
={v(ρ,α)=P+σ。(・〕;ε>o}・P・E(・)・ 、
=匂εE〔α);11ql] <ε,ε>o}. α u{γ(ρ,n,α);P+sロ。α)sρεE(α)}。nεN。 {q・E(・〕;llqll。・・/2n},・・N−{・}, E(α). are called the preneighboエ・hood of p and the preneighbor− The familiesてタ(ρ) and η〔ヵ) are defined γ(ρ,n). The fbllowing Properties have been proved 〔[6],[8]). (1) 〔E(α),Zフ(p,α),妙〔n,α)) fbr eachα εA and (E,ひ(狽),τタ(n)) are ranked spaces・ (2〕P=・−Z鋤k血(E(・)・ZylP・・)・妙㊤・・))iff p・Z鋤たin th・B紐・・h space E(α). 〔3) (E(α),!Yフ(P,α〕,づ〔n,α〕) is co興)1ete iff E〔α) is a. Bana(虫space.〔4)ρ=rLZ鋤k in⑫・ηω・びω)iff th…i・孤・・A・ud・th・t
P=古Z加P瓦in〔E(・〕・V〔P・・)・V(…))・ (5) (亙㌧ τ9(p〕, η(n)〕 is complete iff, foT ever)rα ε ∠1, (E〔α),7タ(p,α),て夕(n,α)〕 is cαmplete. 2. E−valued f皿ctions. 2.1. SiJXple fUnctions . Let 5 be a set,Σ σ一field generated fr㎝subsets of S andμ a finite measure defined onΣ, i・e., 〔5,Σ,μ) is a finite measure space. Let E be the union of rεm]ked vector spaces defined in 1.2. The E_ valued丘mctionαdefined on 5, writtenα:S_→E , is called a si∬文)1e function on 3 if it takes a finite number of values in the fol1σwing foτm : 、THE BOCHN正…R INI!EGRAL FOR FUNCTIONS
㌶謡罐ll(;;‡:嬬鷲畿1 e θ
Asi晦1e f皿ction is uniqUely defined in this fblm. 2・2・ Measurable fUmctions・. The亙一valued f㎞ctionアdefined onσ, written了ご5→E, is.called a measurable fUnction on 5 if there is a sequence {ak}・f・麺1・麺・ti㎝・・n・・u・恒h・t f〔・)=・−Zim ak(・)伽・・…εβ・ Then・f“S→Ei・凪・・ca11・d鵬asurab1・。・β孤d i・訂itt㎝げ・{・た}】if.neces− sary. The fb11㎝ing、prqp《)sitions aτe shσm. . 〔1〕A1血ear cα⑯ination of s麺1e f血cti㎝s onぷis a s麺1e f皿ction on 5. (2)As坤1e fUnction on 5 is a measurable fU皿ct・ion on S. (3)Alineaτcombination of measurable fi皿ctions㎝5is a measurable fUnc− tiOII on 8. : Proof. 「Letア」5『→E↑andσごθ・→・E be measurable fUnctions油idh’are r−1imits °f seqtiences°f・迦P1・imgti。ns{・k}鋤d−{カた}re・pectiv・1y f・r a・…ε5・ i・e・・the「e a「e㎞㎞・t・1.sequ・nces・{γ〔王(・)・−k・・k(・))}・nd{7(θ〔・)・た・βた〔・))} satisfying that,.fbr ead1. k ε 」y and・a.e.8 ε 5,・.there are i’〔k,8) ε 1r alld i”(k,8)εηsuch that{i’〔k js)}and{引’〔k,8)}are increasing with respect to k and ・z(・)・v(ア〔8)細・・た.1〔・))Zμ≧i’(k・・)・ bz(・)・γ(9(・)・k・1・β瓦.1〔・〕)zμ≧z”〔た・・)・ F°「a・e・8εぷ!th・rei・aY(・)・A・ati・輌gth・tE〔・1(・〕)VE〔β1(・))⊂E(Y(・)) (1・2・(ii))・P・tting・k=・たψ瓦(k・の・{・k}i・asequ・nce。f・麺1・㎞c− tions onσ((1))・ Then, the seqUence {V〔(f+9)(s),k,Y(s))} is a fUndamtental seqμence satisfying thqt, fbr eadh瓦, ・ゴ(s)εv((f+9)(s)・k・Y(・))Z拒顧z’(k・・〕・z”(た・・〕)・ In fact, fbrゴ≧max(i’(k38),i”(k38〕) and a.e.ε ε5, II(f+・)(・)一θゴ(叫(。)−ll(拘)(・)一〔・ゴ袖ゴ〕(・〕ll,(。) ・ < < llτ(8)一αゴ〔8)ll・、〔・)+ll・(・)一カゴ〔・)ll・、〔・) ll了(8)一%〔8)ll・k.、(司子 k+1 k+11/2
・+ 1/・2 1/2た. 11・〔8)−bゴ〔8〕 ・、.、(・) 伽・・(f+9)(s)−r一伽・瓦(・)(・・θ・8εぷ)・ Also,λ了fbT any scalarλis measurable on 5.(4)L・t{fk}〔醐b・asequence・f鵬・・u・abl・㎞・ti。n…3・ati・身ing th・t,
f°「e蝕友・the「e i・ase卯・・ce・f・坤1・麺・ti・ns{・ki}〔i・め…海血t な〔・)=r−Zim aki〔・)in E〔α〔・〕)〔α…8ε3)・ L・tf〔・)b・飢r−1緬lt・f{fk〔・)}血亙〔・〔・))f・r・sεS−S・. iP〔3・)=0)・Th・nfi・ameasurable functi㎝㎝ε.
5758
Y.TAG㏄HI
Proof. By the above hypothesis, there is a f血damental seqUence {v(f〔s〕, k,α(8))}〔kεAり sud1 伍at, fbr ead賦’k,.8 ε β_ βo and someゴ(た,8〕, 身〔・)・v(了(・)・k・・(・))z了.ゴ≧ゴ〔k・・〕・ The same consideration as that of Egor◎ff†s T}1eorem on the I・ebesgue integral ・・adS・th・.f…㎝血9・F。・・k−・!・kチ1紐d・k−・!・k’1〔醐,・h・re・・e.蹴Bk C d
c(㌔、S㌻R豊at .
慾〔:慾綴誌1畿㌶{。∴。k.
L・t・・−U,2−。{ coハnFk〔s−Bm)}.一σ一{ハ,2−。〔U三り・ Then, (ii) μ(40) =11⑮), i.θ.3 μ(T〕 =o if T=● − Ao. F・r・・v・ry・ε・・一…』is s。鵬・〔・)…uCh・h・t・εハ急(.)(・一・m)・ Hence, there can be chosen an increasing sequence {k(Z,8)}with respect to Z sudl that k(Z,8)≧nzczx(Z,ゴ(Z+1,8),た(8))∫ (’”〕11・fk〔、,;(・〕イ(・〕ll。(.)・・!2Zチヱ(・ε・・一・・)・ For every 8 ε5Lσo−T・=∠40−50〔μ(θo U㌘)=0,〔ii)) and Z ε N, if k≧k(Z,8〕, then, ’ ll fω一aki(k}(・.)ll。(e〕≦ll・f〔・)−fk(・)ll。〔,)・+}fk(s)一α剛〔・)il。(。) ・・/2Zチ1・・/・kチ1≦・/2Z子1・・/2Z・1。・/・・(〔、),(、i、)).lhis shcrws that・fb「as餌uence°f s麺1e麺cti°ns{dk}={・た姻}(た・め
and a fun(㎞∋ntal sequence {γ(τ(8〕, Z,α(8)}, there is some k(Z,8)〔ZεN) ・ゆth・t・た〔8)εγ.げ〔8),z,α(8))if・k≧k(Z.・)(・・…ε・)・輪,ア・8→互 is a measurable function ol13. 3. Integrals・of E−valued functions on 3. 3・1・ Integraユs of sil呵〕le fUnctions on S・ The integral of a si皿ple 麺・ti・n・a・S→E・f th・fbm血2・1・i・d・fi…d ・・ ZkZ、akV〔Sk〕and i・冊itt・n rSα4i」. A si皿ple f皿ction is also called integrable over S. The followings are shown easily. (1) The integral of the linear coπbination of simple』fUnctions on 5 is e({ual to the linear co迎bination of integrals of those si呵ple fUnctions. (2)For a s坤1e fUnctionαご●→E, there is s㎝e YεAsuch that l[・r.・刺,≦r.II・ll, dU・(3)If’・・3・ε岬52=σmd’・∩5・=〆・「s a d・=’s、α血%、α dU・
’3・2・ Integra150f measurable fUm6tions onぷ. The functiOn f:S→互1 is call・d血t・g・ab1・・ve・5if th・・e i・a・・equence・f・i・rP1・㎞・ti…{・k・’S→E} (kEW) satisfying the fo11σwing conditions.THE BOCHNER INTEGRAI、 FOR FUNCrlONS (i)τ(・〕=告鋤・た(・〕fg…ll・・ε・・
〔ii)輪e ar・飢塒・a・ing・S・q・・nce{MkSk副・nd・(s)・A劔e・・th・・3
・・血t㎏tll飼一・k(s〕ll。(S〕i・Lebesgu・鋤・g・泌1・飢d・ati・fies th籠 r。・ll了(・)一α、(・川。〔。)・… /、Mk〔k・め・ 〔iii)th・・eq・ence{「S・kdv}・f血t・gra1・。f the・麺短㎞・ti。n・i・r−・㎝一 vergent・ .The・・各励な酩μi・ca11・d th・int・9r・1・fτ・ver 5頭訂itt・n毫飾・
We say also f is・an i皿tegral)1e function㎝β. by the conditi㎝ 〔i), there is some f㎞damental sequence of center了(s〕 血・・鵬亙〔β〔・))・飢dτ(・)・%〔・)a・d了(・)−ak(S)・宮(β(S))〔・・…ε5)・F・r. ・〔・)血(ii)・了(r)一・k(・)・E〔・(8))・lh・n・ ll了(・)一・k〔・)ll。〔。〕−ll f(・)一・k(・〕II B(。)1(・・・・…)〔・・Z・(iii))・ Consequently,αmay be considered βwithout loss of generality. So,α is c㎝一 sidered β in the fb11σwing. ifαごぷ→A is a siπple㎞ction, then 〔iii〕 resUlts fr㎝ 〔i) and (ii). Because there is some Y ε44 sudl that 石1(α〔8)〕(二石r(Y) 〔a・θ・8 ε●) and the sequ− ・・ce{fS・k dU}(醐is sh㎝・t。 be a鋼・thy・・eq・ence in th・B鋼・th・pace E〔Y) (1.2.〔ii),(iii〕). 3.3.S㎝e properties㎝integrals of measurable f皿cti㎝s㎝σ.. 〔1) The illtegral of the integrable ㎞cti◎n is u【1iquely defined independently of the dhoice of sequences of si]呵ple㎞ctions. (2) Ihe integral. of the linear’comi)illation of integrable functions.is the linear ccmbination of integrals of those functions. 〔3) Let f:S−》Ebe an integrable fUncti㎝on 5. Then, fbr someαご●→A and s輪α・εA・ll了(・)ll。(。)i・血t・醐1・w・・S・and・th・fb・…桓g掴皿・ity i・ satisfied: .. ll七醜ll。。≦f。 ll f〔・)‖。(。)血・ P・・。f・Let{c・Z}(醐be a・eq・㎝ce・f・麺1・㎞・ti・鵬・ati・fy血9 thd C°㎡iti°品(i)・(ii)飢d(iii)(3・2・)・・Tl・en・II・k〔・〕ll。〔。〕㈹・吐・・ssσf generality, we may chooseα(8〕.in 〔ii)) is a rea1−valued si珂)1e ftmction and satisfies that 〔1’) 川lf(・)11。〔.)−11・・(・)il。(。)1≦. llア(・)−ak〔・)ll。(.)・1霊1麟慧罵’監ご蕊1’Ub°瓢1、Sl・1、=。g←
nt to∫3 f即. Fr㎝(1,),〔ii)and〔iii),for any e>0, there is s㎝eた口 such that 』 . ’ ∫・ll・・(・〕ll。〔。)dU・f。 ll了〔・)ll.。(。声・・/・ and . II 「。 fゴ・ll。。・≦ ’ll fs・k dp ll。。… ./… 5960
Y.TAGUCHI
・Beca田e°f〔i’)・〔iiりand integrability°f 飢d llゐk〔・)llβ〔。〕・
ll f(・)一力友〔・〕llβ(s’)i・血・・卿…ver・皿d・f・−yε〉・,・h・re is s・面… such that f・ 1|f(・〕−bk(釧β(.〕dv<ε・ 在田・this s坤1・f血・ti・n bk i・th・・equi・ed㎝・・ 恥w・聡・・n・㎞。se a・equenc・・f・麺1・㎞・ti…{・た}〔k・N−{°}) Such that, fOr eadhた, 趣..Il f(・)一・k(・)lrβ〔.)一・(・…8ε5)・ 〔皿.)f,・llア〔・)一・k〔・)ll,〔。)・… /・k・ This shows that the conditions 〔i) and (五) of integrability for f are satis− fied. Ifβ(・)is a s麺1e fmction, theTe is anαεAsuch that E〔β(s))⊂E〔α)㍍.ε:’,。::,t惣a:蓋:慧α1’蕊竺}{;、εs≡ζ当晋;1一
Because of the inequalities below: ll∫,・た刺d。≦f。 ll・・II。。dU−∫。ll・k〔・〕ll。(。)dv・ ll∫5了刺。。<∫511 f(・〕li。〔。〕血’・・ ε>O is arbitrarily chosen, so the Teqμired inequality is shown. 〔4〕L・tf・5→Eb・a鵬田・・ab1・fUi・・i。・・lf ll国ll。〔。)i・L・besgu・血t・9r− able over 5 fヒ)r someα:3→、4, then, for anyε>0, there is a s ilnple fUnctionαご8→亙sudh that
∫s ll f〔・)一α(・〕llβ(。)血・ε for someβご3→A. Mbreover, ifβ(s〕is a s麺1e fUnction, then,了is integr− able over 3. P…f・L・t{・k}(κ・めbe a se・lu・・ce・f・麺1・㎞・ti・ns su・h th・t f〔・〕=r−z玩αた(・)(α・…ε・〕・ i・e・・ for some βご3→ ・4・f〔8),αた〔s) εE(β〔s)) and た拠1|了(・)一αた〔・)llβ(.)一・(・・…ε・)・Put
,Tk={・・ll・k〔・)llβ〔。)≦il了(・〕llβ(.)・1}and
カk(・)一・瓦〔・){x〔Tk)}(・)(た・め・“en・Tk・Σ〔k・め・bk(k・のi・a・坤1・fmcti・n孤d
〔1’)趣・・ll f〔・)一力た(・)llβ(。)一・〔・・…ε・)・ For any kεN, 〔ii1)ll f〔・)一ゐた〔・)llβ(。)≦ll了(・)llβ(.)・ll・・〔・〕llβ(。) ll f〔・)ll。(.〕パ1 bk〔・)llβ〔。) ll f〔・)ll。〔。)THE BOCHNER INIEGRAL F()R FUNCTIONS 61 If k,たF≧たo, then
晦・た血㌔・k・dU‖α≦fs ll・ピ・た’ll。δμ
≦{θll・た(・)−f(・)ll。4胆・{Jl%・(・)−f(・)ll♂μ ・1/2た・1〆≦1!2た・+1/2た。くε. then・the「e exi・t・aX拠・k血迦(・〕・Thi・i・th・・−Zi・ rS・k dU i・th・ Tanked space (E〔α〕,1ノ(ρ,α〕,U)〔η,α)), i.e., in 〔互,τ9(p〕,Z夕(η)). Then, the conditign (iii) of integrability fbr f is sat‡sfie尋. (5).1・et{在5→亙}〔た・π)b・asequence。f鵬観・ab1・麺cti。ns・… u(虫 that, for every た, . 』. 〔i’) Hfk(・)ll。た(.)≦”.<°°(・・…ε・〕− Let fごぷ÷E be a measurable f血ction sudh that 〔ii’). f(・〕=i’一’Ziin fk(・) ’(・・…εσ)・Theri・允・・輪・・5鳩ll了〔・)ll。(。〕i・i…卿・・。鴨… .
If theτe is a siXple function corresl}ondent toβ(8)in(4〕. above, then了 is integrable oveT 3. . Proof. By (ii・〕, there is someαご5÷4 such that, fbr every kεN, 了(・)・fk〔・)唖 By 1.2.〔iii〕, lhen, . 1 llf〔・〕11。〔.)− i・e・, forα.e◆sεS. kZgm.II fk〔・)II As fk is measurable on these fac.ts and 〔iり, 了(・)−fk(・)ε恥〔・))(a.θ・8εs). Il・fk(8川・k〔・)=ll・fk(・)ll・〔。)・ II・fk(8〕ll・k〔・〕1≦ll了(・)−fk(・)ll。〔。)(・…8εβ)‘.編。 麟1・li。。鵬お一・。。n.⑭. by
ll了(・)ll’。〔。)i・狐i泣・g・ab・・fm・ti・n・・ぷ・. by (4) above, fbr a皿yε>0』, there 工s a si珂ple fUnctionαごぷ◆E such that ∫・ll f〔・〕一・(・)llβ(。〕cl・i・εfb…rne B…A・・fβ(・〕. i・a麺・・fmc− tion, then f is illtegrable over 3. ’ Acknowledgemnents. The author would like to express her gratitude to Prof. S. Nakanishi fbr suggestions and valual)1e・dユscussions and to Prof. Y. Nagakura for 1∞king thrcugh this note and examining Proofs of Proposltlons・ ,62 Y.TAGUCH工 [1] [2] [3] [4] ]] に∨∠0 [[ [7] [8] REFERENCES S.Bochner: InVegration von正Unctionen, deren Werte die Elemente eines Vektorrauines sind, Fund. Math. 20 (1933), 262−276. H.G.Gamir, M.De Wilde, J.Schmets:Analyse Fonctionnelle, t.II, Bir㎞i辿ser Wrlag Basel und Stuttgart〔1972). K.KUnugi:Sur les espaces complets et r6gulibrernent co呵)1ets,1, Proc.Japan Acad. 30〔1954), 553−556. K.Kunugi:Sur la m6thode des espaces rang6s,1, Proc. Japan Acad.42(1966), 318−322. 1.Miyadera:Kansukaiseki, Rikoga㎞sha〔1972〕. ・ S.Nakanishi:On the strict union of ran]ked皿etric spaces, Proc. Japan Acad. 50〔1974), 603−607. S.Nakanishi:Integration of fUnctions with values in a convex ranked space Mathematica Japonica,23,no.1(1978),85−103. S.Nakanishi:On ranked union spaces, Mathematica Japonica, 23,no.2〔1978), 249−257. SCIENCE UNIVERSITY OF T〔)1(YO .