PR■TFTBUNGSOFTHE A凶F回uC▲HMAnBEMATuCALsoC1ETv vblmtelZO・NumbET2.F■bm□Jy1994 NON-COHEN-MACAULAYSYMBOLICBLOW-UPS FORSPACEMONOMIALCUIWES ANDCOUNTERExAMPIESTOCOwSIKSQuESrlON SHIROGOTO,KOJINISHIDA,ANDKEI-ICHIWATANABE (CommunicaledbyEricFnedlandeT) AnsTRAcT・LetA=AIIJr,γ、Z]]andkⅡ、]befbnnalpowersenesnngs ovemneldと,andletn>4beanime8ermchlhat〃差Omod3・陸t o:八一A【[nidenotethehomomomhismo「昨algebmsde6nedbyp(X)= 77n-コ,。(y)=TW-z)河,and。(Z)=781,-3.WepuIp=KCT。、Then Rn(p)=①l三op(i)isaNoetheriannngi「andonlyircM>0.Henceon COw3ikosquestionthcに画℃counIeにxamplesamongthepnmeidcalsdenning spacemonomialcurves,too. LINTRoDucTIoN I心t』=k[[X,Y,Z]]andS=k[[刀]befbrmalpowersenesrmgsovera he1.k,andlet〃,,〃2,and〃3bepositiveintegc応withGCD("I,〃1,〃〕)=1. Wedenotebyp(",,〃2,〃3)thekemelofthehomomolphismp:八一sof応 algebmsdefinedbyO(X)=T"1,。(Y)=T"2,and。(Z)=か,、Hence p=p("肋〃1,〃3)istheextendedidealintheringAofthedehningidealfbr themonomialcurvex=!"1,J=ln2,andz=rm,inAii・ AUttlemorcgeneraUy,letpbeaprimeidealofheight2ina3-dimensional r巳gularlocalringA・WeputR`(p)=E">op(")T〃(herETdenotesanin‐ determinateoverd)andcaUitthesymb6iicReesalgebraofp・Then,as isweUlmown,R`(p)isaKrullringwiththedivisorclassgroupZ,andif RS(p)isaNoetherianringitscanonicalmoduleisgivenby[R,(p)](-1)(Cf, e,8.,[12,CoToUary3、4]).ConsequenUyR,(p)isaGorensteinring,onceitis COhen-Macaulay、TheTeadeTsmayconsult[2,3]fbracriterionofRs(p)being COhen-Macaulay,wheにsevemlexamplesofprimeidealspwithGorenstein symboUcReesalgebmsaJEexplomed,too・ Nevertheless,aswashrstshownbyMorimotoandthefirstauthor[8],R`(p) arenotnecessalilyCohen-Macaulayevenfbrthespacemonomialcuwesp= p(",,〃2,〃]).ThisrBseaJchisasuccessionto[8]andtheaimistoprovidethe fbllowingnewexamples. Receivedbytheedjto届January22,l9Z2and,hMUvisedfbrm,May28,1912. 1991A血KA2mpUicsSbubjepCⅢエfsi〃mIio"・PrimaIyl3HO5,l3Hl3,l3H15;Secondmyl4H20, 14J17. Theauthorsa定paniallysupporledbyCmnt-in-AjdlbrCO-opcmliveRescar℃h、 、I994AmmcmMmhemmcnlSo句eoy OOOZ・”W94SLOO+3.29perp■GE 383 牛ⅡローIrtJ1■■・・・]④エヨ0口-・早足凸い七勺・・□rr0■砂1㎡殆・・Tチー引汁Ⅲ岬’‐(▼が西 s,GOT0,K.NISHIDA,ANDlLwATANABE 384 Theorem1.1.Cho“eα〃i"(…「〃z4solhar〃姜Omod3q"。”lP= p(7"-3,(5"-2)皿8"-3).Lelc=Y3-X"Znα"。(zsFⅢmelAalchA=P>0. 711I2nlhe花2xjslsq〃eleme"【AEp(3p)saljqb'i"glAee9Ⅸα"ly lengnhU/(x,c,A))=3p・lengthW(x)+p) 1F・・八・千・・・.叩小咄排朴r・LJⅡかく、命f】1Jか‐P設いJIL、嵌喉凹肝血幸一㈹肛別仏器篭眠Ⅲ、皿睡攝払、Ⅲ‐隅脚fu咄蝿即懸山畑砥Ⅲ吋聰鰯幡ⅡⅢ鋤 ノbrα'、,xE(X,Y,Z)Alp.】"pα"たwlmR`(p)isαノVb2lhemz〃rmg6m〃α のhe汁Mzczzl(lbzy・ Heにletusnotethattheidealpintheabovelheorcmisgenemtedbythe maximalmino応ofthematrix (’V郷:二|); hencepisaselfL1inkedidealinthesenseofHerzogandUlrich[6,CoroUaly 1.10】,thatis,p=(ノ,g):pfbrsomeelemems/,gEp・Roughlyspeakins seMLlinkedidealsenjoymoreexceUentnaturesthanthoseoftheidealswhich aICnotselfLlinked、FOrmstance,thesubringsA[p7,p(2)T2】ofR`(p)are alwaysGorenstein,ifthecoITespondingidealspa泥selfLlinked(see[6,Proof ofTheorCm2.1]).Fromthispointofviewitseemsmthernaturaltoexpectthat thewholeringsR`(p)areGorensteinatleastfbrselfLlinkedidealsp;however, theanswerisnegativeasweclaiminTheo応、1.1. 。■ロロⅡ■■11|ケト■■■PIBL2■UⅡ日日p■・FUI■■IⅡ.Iir 1,[8]Morimotoandthehrstauthorconstmcted,fbreachprimenumberP, spacemonomialcurvespwhosesymbolicReesalgebrasR`(p)areNoetherian butnotCohen-Macaulay,ifthecharacteristicchAofthegroundheldlcis equaltop、Neverthelesstheirexamplesare〃olselfLlinkedand,fmrthelmore,it isnotclearfbrtheirexampleswhetherRs(p)areNoetherianornotinthecase whe妃thecharacteristicisdiHbremfiomthegivenprimenumberp,whileour examplesareNoetheriana、dnon-Cohen-Macaulaywheneverchk>0. ThisadvantagenatumUyenablesus,passingtothereductionmoduloprime numbe応,toexplo定thecaseofchamcteristicO,too,MoreoveT,somewhat surprisingly,asanimmediateconsequenceofTheorem1.1wegetthefbllowing counterexamplestoCowsik,squestionI1],thataskedwhetherthesymbolicRees algebmR`(p)beaNoetherianringfbranyprimeidealpina定gularloca1ring A: COroUmy1.2.L21p62aprim2iUlbzzノslaleu!』〃、CO花、1.1.7111mR`(p)jS nolqノVbaAmα〃mUgbヴchk=O WhenCowsikraisedthequestion,heaimedaIsoapossiblenewapproach towardtheproblemposedbyKronecker,whoaskedwhetheranyirrCducible allinealgebmiccurveinAecouldbedehnedbyn-1equations、I、fact, Ⅶ波.‐研玲・如叩・I.n㎡. ‐DL0000■Ⅱ□らJ■仏叫Eu昨Pu・b9IⅢIDIⅢ : : Cowsikpointedoutin[1]thatpisaset-theo正ticcompleteinte唾ction,if R`(p)isaNoetherianringandifdimA/p=1;however,asisweUknown, whileKroneckeT、sproblemremamedopenonCowsick,squestiontherewas al肥adygivenacounterexamp1ebyRoberts[,].Becausehislirstexampledid notrCmainpnmewhenthelingwascomp1eted,herecentlyconstmctedthe secondcounterexamples[10]・Theyareactuallyheight3primeidealsinafbrmal powerseriesringwithsevenvariablesoveraIield;now,providingnewand simplercounterexamplesamongtheplimeidealsinthefbnnalpowerseries nngQ[Pr,y,Z]],ourCoroUaryLZseltlesCowsik,squestion,thoughitsays nothingaboutKronecker,sproblemitself  ̄ NON厄OHEN・MACAUlAYSYMBOUCBLOW・UPS 。85 TbesimplestexamplegivenbyTheoremL1istheprimeidealp= p(25,72,29)=(XIl-YZ7,y3-X4Z4,ZI1-X7Y2)in』=IC[[X,Y,Z]]、 ThesymbolicReesalgebraRs(p)isaNoetherianTingbutnotCohen-Macaulay, ifcM>0,andRs(p)isnotaNoetherianring,ifcM=0.Therefbre,the symbolicblow-upR,(P)=Z">oPい)T〃isnotahnitelygeneratedQ-algebm fbrtheprimeidealP=(XlI-YZ7,y3-X4Z4,ZlI-X7】'2)inthepoly‐ nomialnngO[X,y,Z],too NowletusbneOyexplainhowthispapeTisorganized・TheproorofTheorem 1.1andCoroUaryl,Zwillbegivenin§4.Section3isdevotedtoareduction techniquemoduloprimenumber5.1,§ZweshaUsummanzesomepldiminary stepslhatweneedtoproveTheorem1.1andCorollary1.2. Otherwisespecified,inwhatfbllowsletA=k[[X,y,Z]]denoteafbrmal powersenesrmgoverafixedfieldk・止tm=(X,Y,ZMbethemaximal idealofA・Wedenoteby2AW),fbranA-moduleノV,thelengthofノV、FOr agivenprimeidealpinAweput R`(p)=ZP1jD7mcA[刀, 、>O Rj(,)=Zp⑩17m(=R`(p)[丁-1])こ」[7,T-IL jHEZ Gs(p)=R;(p)/丁~IRj(p) whereTisanindeterminateoverA. 2.PRELIMINARIES FirstofallletusrecallHuneke,scriterion[7]fbrR`(p)tobeaNoetherian rin8FbrawhUeletい,、)denotearegularlocalringofdim』=3andlet pbeaprimeidealofAwithdim』/p=1. Theo肥、2.1[71.〃rhaで2xjs『雄me"砥/Ep(I)α"dgEp(、)wilhp“irjve j"legF7Tノα"dms84垣hlノ、【 2A(』/(x,/,g))=ノ、.cAu/(x)+p) ノbrmmeXEmlp,肋enR`(p)jSdzノVDah2rm〃〃"gリゲリiemAeノieItfA/mjS m/i"ilelrhecD"ve応ejSdMsolme、 ThenextpropositionallowsustoarbitrarilychoosetheelementJrinTheo‐ rem2・LTheresultisimpliciUyfbundin[7,ProofofTheo1℃、3.1】andisdue toHuneke Pmposition2.2.Lα/Ep(ノ)α"‘gep(、)(ノ,m>O)α"‘αmswmerAm 2A(』/(x,/,g))=ノ、・2」W(x)+p) ノbrsomexEmlp.〃enlhe”ovee984zz"〃holtisノb「α"yxEmlp・ PrUqfWemayassume/=、、Then(/,g)Aisareductionofp(、);actuaUy, [p(、)]2=(ノ,g).p(、)(Cf[Z,PToofofProposition(3.1)]).laR=Apand n=pAp・Thenastheideal(/,g)Risareductionofmmandas(R,、)isa 2-dimensionalregularlocalring,weget 2尺(R/(八g)R)=ど鵬)R(R)=elh(R)=、2 ポニ 。■C宮⑤⑭四四コ、一戸』ロ蒄二 唾這』畠⑭⑨』堂⑭』⑨吾。二塁U一周山⑭』口印』◎曼弓⑫ニト・肘』昌凹』u畠】宜己○扇哩囲冨圏彦」。。』。』⑭EC二爵三.田一 .「-C昼Ⅵ』Ⅵ『二碧夢(』IC層)ロ山切已目■ (》)色山国①日。⑫皇哩僧陶Ⅱ両。烏二:便(』‐・這)二・代(》)曰(」鼬囚山侭目珂冒口 甸呂『⑪冒呵。⑭。忌昌』.(出俸浅)□◎目目。『一旦ロ圏昌一・倉旦。p:ご目(為(浅)}『 ⅡR』⑫曰.(』I・層)色(』)二一」蝕囚Ⅱ(。昼)已輿)冒雷.[oEv痘Ⅵ【{軍ト(唇}ロ}]『Ⅱ(。)竜葛昌 [(寸)(炉.、)円◎富⑪。□。』四ぺ]湯。⑭シ⑤二⑭彦目⑭ニト,昏圏旨〔己③二』⑪日。鵠く一筥○2国 .[蘆V踵Ⅵ|{匡烏{■)&}]『迅蘆借□函・功・Np●三碗C竺冒由 .E|◎這忌巳ミロ。:冒弓日云苔一、罠 愚冨鳶鍋(□+(浅)「『)『》.(ロミー富)Ⅱ((『軸・奈鶉)(更)『》曾畠二⑭彦辱((一軸毎・曇淫)}『)『》 十((昂jへ卍)へ『)『》Ⅱ((恥辱Y浸)へ『)『》場目輿〕昌目員僧.(・層I這一色山一”昌冒 (。)ご○昌一蝿勗Ⅲ恥竺泪夢⑭逹戸・[(御)(ト.、)ロ。冨的。□。』円く]託二(色EIE)巳(鰯十(lIE)二・ Ⅱ(眉)ロ⑭。目⑭二参《((輔(。)Ⅵ(層)且冨昌[(寸・向)■C君mCp2由パ}易ロ』畠○藍島這Ⅵ。冨 鰡目毎揖.(昌十(農)「『)『》・蔓Ⅱ((殉。←渓)}『)ご]甸昌二目⑫(E)a山”一輿】葛貰童& 、蝿山置合ご』ミミlCE・で.【■E一目当 昌冒員國②二豊蜀閂 。(邑十(浅)」『)『》・・蔓Ⅱ((勗’(鶉){『)『》冨皀。⑬(。E)邑山勗旨①【5[の目 ⑭、○.二○℃■甸上喝眉目Ⅱcミヨ旦垈夢壹・○朴化喝蔚邑⑭眉扇患で宮呵{(負+(涜)一『)『》・ミ Ⅱご旨○聖夢祷.([、]筥○)巴畠⑭冒弓。シ富⑫。竺餌局』(で自呵(』ご毎」己隼((ご《ご閨⑫回参 Ⅱ((閲。《漢)「『)ご旨邑二○コ⑰(E)a山恥、一国山這v○}Ⅱ蝿】②目.((Qござ) Ⅱ&典〕5二)(N・渓-.国十回済Ⅱ。ご目。『(Nご門’一s十己璃Ⅱ凸碆菖済←・渓I『託十(N ・(一鵬鮒騨) 自巨&⑭二』◎浅恒苗目甸』◎圏自渭■百日宮国■②邑苣ロ⑭】圏⑭5幽摺ロ苗邑 ⑭【昌鵠甸冒三四参.一{&冨二彰昌。(蟹Ⅱ(且+(N)へ詞)『》□目(胃Ⅱ(邑十(湯)}『)『》 二竃Ⅱ(a+(※)へ『)『》85二)[[N・缶鎬浅]]毬Ⅱ『属(昌辱畳今【竃)色Ⅱ色の着]ご園 『Ⅱ(曾肉ミミ)QQo昌冨留乱③旨温良愚且us萱○爵(昌二竃芯[参。白●夢 .{川竃言』負勇昌冒)呈下愚琶U鼬ご .【lミ+}Ⅵ筐Ⅵ[壱」負高昌冒〕旬ミー§言。餌&(鐘)&+(閏く)奇(、) (丘)二十(的。(){『、■曰。(廷)a+(恥)一『.(■)ロ+((){更品冨憧四ミ、量ご察E隅軸、竃ご合一烏』 A1層十一Ⅵ鐘Ⅵ|{息(電)&}島冨置き禺魯(色)宮冨篭些ご‐『里』⑪鷺ご皇』愚量』息澤建 恥鐘撞冨聖固薗己・口唇(色)均筥(【) ・三豊冨冨苛色』国璽へ。》》増産8 。ご曽冨ミミ蔓》愚壱・『副』愚息言昌弓増閣、§』遍臼.[劇]呵嗣昌圏[ご胃 .。。』(一百四①』』『⑭二一⑫』②ニ豊C目⑬二一②曰・【.N[眉呂 ・良EUH旨⑪日⑪一⑭百吋』& 。。⑭二P日凹ご目彊巴忌日⑭一④⑭己」◎旨5]眉普恒(員。届ロP】CD輿)ロ皇)訂一二輿)昌邑 ‐5二.Q回①PC](a)雪』皇宮◎窟壱○“⑭畠函召。旦湯己目釘君二圏Z。】。。[【]日 (邑十(麓)「『)ぜ.【屋Ⅱ (□十(麓)一雨)て》。(電(“(』){“)]》Ⅱ((軸(』(麓)「『)ご ]圏一宮○畳二二日』。[寓{・弓三]面目円眉昌豐冨己冨②昌苣⑪馬二⑪夢《吟門レト』シ C酉、 Ⅱ::』&:二』・雲三昌一二目皇。】・言(閨)零℃目(閨)“(“.一四;言 四項廷Z式房迂参一出口z定ぐ口冨圏z望.CPC、.、 H・・一 霧蕊 …二等f扇:愚…宇尋雪驫王讓專罠薦零轌霞藍韓蘂霜蕊冒韓謹轤謹璽露藥喜露琴蕊 ;11艸可=」七二=話邑~里由 NON・COHEN・MACAULAYSYMBOUCBLOW・UPS 387 NowrCcaUthatc=γβ+β,mod(X)andweget 2Au/(X,c,9192))=(β+β').g`(』/(x,y,9,82)) =(β+β')・2AU/(X,y,go))=m0.2Au/(X)+p). Hencetheelememscandglg2satisfyHuneke,scondition(2.1)sothatc andglsatisfythisconditionasweUlnfact,because2A(A/(X,c,9,唖))= 2A(A/(X,c,8,))+2A(』/(X,c,92))=m0.2列(A/(X)+p),wegelbythein‐ equalities2A(」/(X,c,91))三i・[’1W(X)+p)and2A(A/(X,c,唖))三 (耐o-i)・gAU/(X)+p)thatノ`,(A/(X,c,9,))=j・山(A/(X)+p).Thuswe havejE夕,whichcontmdictstheminimalityofmo・ ThenextresultisthekeyinouTproofofCorollary1.2 ComUmy2、6.ASSWmelhqlβ+β'=3α"dlAaj31〃,、Ldpbeap"m2mJ碗be「 ノbrMijdiwe(zsswmelhα〃h罪axmanekme"lgEppp)sα【幼mglAe珂凹α"〃 2A(」/(X,c,g))=3p・(`,(』/(X)+P).、“ヴgT3ped[{p(")T''},≦,,<卯],we hqvemo=3口"。R`(p)=A[p7,p(Z)72,p(3)T3l PmqfAs2AU/(X)+p)=〃,andasc=Y3mod(X),wehavethat 2A(A/(X,c,go))=、on,=3.2A“/(X,Y,go)). Hence31mo,because31〃Ibyourassumption・Iamo=3m,、Thenas mol3pby止mma24,weseemI=1oTp・Ifmlwercequaltop,thcnmo= 3PandsowemusthavebyProposition2.5thatgT3PEAI{p(")T"},≦"<3pL whichcontmdictsourstandardassumption,Thusmo=3andwegetby[2, Proposition(3.7)(4)]thatRs(p)=A[p丁,p(2)T2,gOT3]. 3.REDucTIoNTomEcAsEwHEREchA>O Ia〃山〃2,and〃3bepositiveintege応withGCD(",,〃2,〃3)=1.Let C=Z[X,Y,Z]andZ[nbepolynomialringsoverZ・Wedenoteby9D:C一 Z[刀thehomomorphismofrmgssuchthatp(X)=T"',。(Y)=T"ユ,and 。(Z)=T"3.匹tI=KerpandconsidertheringCtobeagradedringwhose graduationisdehnedbyCb=Z,qIヨX,Q2ヨァ,andChjヨZ・Then thehomomonphismppreservesthegraduationsothatJisnatumllyagmded pIimeidealinC、 FOragivenheldk,4k=k[[X,Y,Z]]denotesafbrmalpowersenesrmg・ WeputBk=kIjr,Y,Z],thatweshaUidentifywithA②zC、止tpjtdenote theidealp(",,〃1,〃〕)conside冗dinAA;hence,pJt=“〃WeputBt=Jα・ ThusPhisthedenningpnmeidealofthemonomialcuwex=r"',y=『"2, andz=["jinAi, Thepurposeofthissectjonistoprovethefbllowing Theorem3.1.A"ⅨmeZharR`(pq)jSqノV02lherWz"rj"8,11“ピルe庵exな【p“"jv2 j"【率晒ノV,、α"。e佗me"us/,gq/J(、)swcMiat〃p曲aprjme”m62r α"。〃pzjv,wEaノMuys他泥 (1)p『)=J(噸)。&。"‘ (2)2Ak(`4k/(x,/,g)Aと)=、2.2A‘(八k/(x)+pk) ノbr1heノi2IWEZ/pZ、 PmqfWeputB=80,P=化,and〃=(X,γ,Z)β、ThenasA= AQisafmhfUUynatextensionofBM,thesymbolicReesalgebraR`(PBM li1 388 ! S・GOT0.KNIgHUDA・ANDXWATANABE isaNoethelianlingtoo;therCfbre,byTheorem2・landPToposition2・Zwe maychoosetwoelements/,gE(PB」v)(、)withmapositiveintegersothat 2B"(BM/(X,/,g)B")=伽2.2恥(β"/xBM+PBM).LetⅣ=(X,γ,Z)C、 ThenasCAr=B〃andJqv=PBAf,wecantake/andgtobeinノ(、). 陸tsECVbeanelementsuchthatsI(、)CJm・WeexpandO(s)= ELsjTjinZ[T]withsb≠OandchooseapnmenumbcrpsothatPl3.. Thentheelement了=1②sofBk=k②zCisnotcontainedinPi=ノBAand 5沖)BjEJ碗必=JW0・HenccJ(凧)BkEB(碗). WenowTecaUthat[(PB")(、)]z=(/,g)BJM・(PB刑)(、)(Cf[2,Proofof Proposition(3.1)])andchooseanelement5=ご(X,Y,Z)ECVVsothat §・[I(、)]2E(ノ,g)C・I(、).ThenifpisaprimenumbeTandifpl5(0,0,0), theelement§=1②:ofBkisnotcontainedinMルー(X,y,Z)BAand F・[”)Bk]ユニ(/,g)Bk・I(、)Bk・Thuswehave[I(、)。k]2=(/,g)」ルノ(''Mk indk, Letuschooseapnmenumberpsothatpisanon-zero-divisoronD= C/XC+J(、)(thischoiceispossible,becauseAsszDisanniteset).Thenas Xisanon-zem-divisoronC/I(、),wegetacommutativediagmm O I O-C〃(、)当C/J(、)-D-O pIP↓p1 O-C〃(、)当C〃(、)一D-O withexactrows・ConsequentlyXisanon-ze「o-divisoronBk/I(、)Bk,while Pl:=、/7T祠万万because〃二J(、)BにBk;theにfbrc,thegradedidcalJ(、)Bk is且-primary(noticethatdimBk/J(、)Bk=1,asdimBk/PX=I)andsowe havCthatPW")EJ(碗)Bk、 SummarizingtheaboveobservationsandchoosingapnmenumbeTpsothat PISb,Pl《(0,0,0),andpEUqE…q,wegetthatpF1=”]Albandthat [pFml]2=(/,g)AI`W1fbrthehcldk=Z〃Z・Th…condasscrtion(2)now fbUowsfiommeequality[pF1]ユー(/,g)」ルpF1simUmlyasinthcpm・fof Pmpositionユ2.ThiscompletestheproofofTheo肥、3.1. 4.PRooFoFTHEoREML1ANDCoRoLLARY1・Z Letn≧4beanintegersuchthat〃差Omod3andletkbealield・In thissectionweexploretheprimeidealp=p(7〃-3,(5〃-2)恥8〃-3)in 』=k[[X,Y,Z】]・ThepurposeistoproveTheoreml・landCoroUary1.2. Firstofallr己callthatpisgeneratedbythemaximalminorsofthematrix (顎二葱二|) (Cf[5]).WeputQ=Z3"-1-Xz"-1YZ,6=X3n-l-YZz''-1,andc= y3-X風Z〃(hencep=(α,6,c)).NoticethatanypairofzJ,6,andcfbrms aregularsystemofparametersinAp,sincethereistheobviousrclation (4.1)X"α+YZb+Z2"-IC=0. NONCOHEN・MACAUしWSYMBOUCBLOW・UPS 389 Let d2=X"-ly5Z"-l-3Xユ"-1YzZ2'1-1+X,"-2y+Z5"-2, .3=_X]"-ZY7+2X"-lY5Z3"-1+X4"-ZY4Z〃 -5jr2Jv-lY2Z4"-1+3X5"-ZYZz'l-X8"-3Z+Z7"-2, .』=Y8Z2"-2-4X"Y5Z3"-2+X4"-1Y4Z"~!+6Xz"y2Z4"~z -4X5"-lYZz"-1+X8lu-2-XZ7"-3. ThenadirCctcomputationeasilychecks X"d2-y62+Z'w-lqc=0, (4.2)Xn-Ib2c+qdz-Z"-ld3=0, Xd3+Ybc2+ZdB=0. HcncediEp(2)andd3,djEp(3). ThenextlemmaisaspecialcaseofmuchmoTegeneralresults(Cf[3,CoTol‐ 1ary(2.6)]and[4,Theo妃m(5.4)]),however,webrieflygiveadiJEctplDoffbr thesakeofcomplcteness・ 陸mma43.p(2)=p2+(。z)α"。p(3)=pp(2)+(。〕,。』). PmqfAs(X)+p2+(。h)=(X)+(】'6,y4Z2"-1,y3Z3n-l,Y2Z4"-2,Z5"-2), weget 2八(」/(X)+pZ+(の))=3(7〃-3). Ontheotherhandbytheadditivefbrmulaofmultiplicityweget [ん“/(X)+p(2))=24,(AP/p2Ap)・2A(A/(X)+p)=3.(7〃-3). Hence2A“/(X)+p(z))=2Au/(X)+pz+(d2))sothatwehave(X)+p(2)= (X)+p2+(ぬ),whichimpliesp(2)=p2+(。Z)+Xp(2).Thusp(2)=p2+(。z) byNakayama,slemmaConsequently (X)+pp(2)+(d3,.,=(X)+(Y,,Y8Zm-2,y7Zz"-1,Y6Z3"-1, y5Z4"-Z,Y3Z5"-2,yZ7"-3,Z7"-2), whence 2A似/(X)+pp(2)+(ぬ,。』))=6(7"-3). BeCaUSe2A仏/(X)+P(3))=均,(AP/P3Ap)・(』仏/(X)+P),WehaVe 2`(」/(x)+p(3))=2`W(x)+pp(2)+(。〕,。』)) and,thus,p(3)=pp(2)+(。],`』)asrEquirCd Pmposi回0,4.4.,2㎡"9A/(c)+p(3)心〃αCDAe"-MzcmUm'. n℃q八匹teh“/(c)+p(3))dcnotethcmultiplicityofXAinA/(c)+p(3). ThenasAp/cApisaDVR,wegetbytheadditivefbrmulaofmultiplicitythat e3`W(c)+p(3))=3(7"-3). 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ThusAT"EAI{p1)Ti}!≦i<3小because2m≦3pbyourchoiceofp・Sincc 317〃-3byourstandardassumption,wegetbyCoroUary2、6thatR3(p)= 』[p7,p(z)T2,p(3)T3].Consequentlyoneoftheconditionsstatedin[4,Theo‐ rem(6.1)(2)]mustbesatishedfbrthedataα=恥β=1,γ=恥。'=2"-1, β'=2,a、。γ'=2"-1,whichisobviouslyimpossible・HenceR`(pk)cannot beaNoetherianring,ifchk=0.ThiscompletestheproofofCoroUary(1.2). Remark4、5.丁hesameproofworksfbrthcfbUowingexamples,too・Let〃Z Sbeanintegersuchthat317〃-10and〃菫-7mod59・唾tp= p(7〃-10,5"z-7〃+1,8〃-3).ThenRS(p)isnotaNoetherianring,if cM=0.Thesimplestexampleofthiscascisthepmmeidealp=p(25,91,37) =(Xl4-YZ7,Y3-X5Z4,Z11-X9Y2)inQ[[X,y,Z]]・ThecorTcsponding matrixisgivenby (李郷) REFmENcEs LR・Cowsik,SpmMiどpowFPT2lwjIhe"皿mbaqntlillillg印lmfio“,A1gebraanditsAppli‐ catimu9(NewDelhi,1981),I△ctuにNoIesmPurandAppl、Math.,vol、91,Dekker,New York,1184,ppl3-14. 2.s・Goto,K-Nishida,andY・Shimoda,がEGOクゼリDsleun"麺qハワノ、“"CRC直mlgPb“jbr 叩quFcw「uG3,J・Math、SOC・Japan43(1991),465-481. 3.-,71iEGol■PzsTei""“q/lheSymbo比blbw4Ps/brCPTmi"SP“FmO"omml“、'",Tm、5. Amer・MaULSoc.(Ioappear). 4.-,7bpj垣so〃〃m如比R2画sqlgebmsjbrjPaPmo"omiqlcwn'as,NagoyaMaIh.』.】型 (1991),99-132. 5.J・Herz09,GF"eFmolTam'Pla[mJnsqm6eWα"sBmlgmUPsqmsemigmIWi"9s,Manuscnpta Math3(1970),’75-1,3. 6.J・HemogandB・U1nch,生峡lj"kgulcwn'2sj"gwlmlj",NagoyaMath.』、120(1190),12,153. 7.C・Huneke,磁ル"【山mionsq"dSym6olicpowe応,MichigamMath.』、34(1,87),213-318, 8.M.MonmotoandS・Goto,jVb昨CbJbe〃MnumJmy〃m加肱blmwUpsノb「Spa囮Pmo"0mmノ cwrv垣s,Pmc、AmcT・MaUl、SCC、116(1,92),305-312. 1 392 S,OOTODILMSHIDA,ANDDLWAT汎NABE ,.P・RObenS,AP"、Blu上UWnqpOO′"omjZZノ「ilugMbosEEym6o化bbw-叩画n0JノVbaノbmm, Pmc.Amer・Math、SOC、94(1985),589-592. 10.-,AnjpUimleb、8F"Fml“nmboIiどblbwJpsjnq“wF「SF河2S〃嘘α”α"fwrmmr死恐 qmp卿o疏仏mlsノbImeelllhp”6t耐,J・Al8eb垣13Z(1990),461-473. 11.J.P・Sem,Ajg色6だわ、lP:MMllP“ldsp3rded.,Lエctu定NoqesinMath..v01.11,SpnngET迫 Verlag、NewYmkp1975. 12.A・Simi5andN.V・Tnm&71bFdiF“「clh野8m"q/ofpma〃qMJym6c此blbwdps,Math・ Z.】兜(1988),479-491. DEPARTMEluToFMATHEMATucs,MEuJHUIwuvERsuTY,HIoAsHIMmh、TAMA-Ku,KJLwAsAnu-sHl, JAPAN GRADuATEScHooLoFScIEUwcEApIDTEcHNoLooY,CHuBAUNIvERsITY、YAYoI-cwo,CHIBA・sH1、 JAPAN DEPARTMENToFMATnuEMATIcALScIENcEs,TOxJuUNuvERsITY,HlRATsuKA-sHu,KANAcAwA, JAPAN ニー---
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