00291nam a2200121Ia 45000030006000000080041000060400015000471000020000622450035000822600023001175460012001400050017001520STCL150530s9999    xx            000 0 und d  aSTCLcSTCL  aPetrovsky, I.G.  aPartial differential equations  bIntersciencec1962  aEnglish20220125165942.0