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1、Sub-RiemanniangeometryandLiegroupsPartISeminarNotes,DMA-EPFL,2001M.BuligaInstitutBernoulliB^atimentMAEcolePolytechniqueFederaledeLausanneCH1015Lausanne,SwitzerlandMarius.Buliga@ep
.chandInstituteofMathematics,RomanianAcademyP.O.BOX1-764,RO70700Bucuresti,Roman
2、iaMarius.Buliga@imar.roThisversion:October31,2002Keywords:sub-Riemanniangeometry,symplecticgeometry,CarnotgroupsarXiv:math.MG/0210189v331Oct200212IntroductionM.Gromov[13],pages85{86:"3.15.Proposition:Let(V;g)beaRiemannianmanifoldwithgcontinuous.Foreachv2Vthespace
3、s(V;v)Lipschitzconvergeas!1tothetangentspace(TvV;0)withitsEuclideanmetricgv.Proof+:StartwithaC1map(Rn;0)!(V;v)whosedierentialisisometricat0.The-scalingsofthisprovidealmostisometriesbetweenlargeballsinRnandthoseinVfor!1.Remark:InfactwecandeneRiemannianmanif
4、oldsaslocallycompactpathmetricspacesthatsatisfytheconclusionofProposition3.15."Ifso,Gromov'sremarkshouldapplytoanysub-Riemannianmanifold.Whythenisthesub-RiemanniancasesodierentfromtheRiemannianone?Hereisalistoflegitimatequestions:Howcanonedenethemanifoldstructu
5、re?Whoarethetangentandcotangentbundles?Whatistheintrinsicdierentialcalculus?WhyarethereabnormalgeodesicsiftheHamiltonianformalismonthecotangentbundlewerecomplete?IfthemanifoldisacompactLiegroupdoesthetangentbundlecarryanaturalgroupstructure?Whataredierentialfor
6、ms,deRhamcochain,andthevariationalcomplex?Considerthegroupofsmoothvolumepreservingtransformations.Whydoesthisgrouphavemoreinvariantsthanthevolumeandwhatistheinterpretationoftheseinvariants?Thepurposeofthisworkingseminarwastoexploreasmanyaspossibleopenquestionsfro
7、mthelistabove.SpecialattentionhasbeenpayedtothecaseofaLiegroupwithaleftinvariantdistribution.Theseminar,organisedbytheauthorandTudorRatiuattheMathematicsDe-partment,EPFL,startedinNovember2001.Thepaperisbynomeansselfcontained.Foranyunprovedresultitisindicatedthep
8、lacewhereacompleteproofcanbefound.Thechoiceoftheproofsisratherpsychological:someofthemhaveageometricalormixedgeometric-analyticalmean-ing(liketheproofofHopf-Ri