00298nam a2200121Ia 45000030006000000080041000060400015000471000018000622450058000802600009001385460012001470050017001590STCL150530s9999    xx            000 0 und d  aSTCLcSTCL  aElsgottis, L.  aDifferential equations and the calculus of variations  c1973  aEnglish20220125165942.0