00385nam a2200133 a 450000500170000002000150001708200160003210000220004824500370007026000350010730000270014249000550016963000270022420251203090945.0  a0124547508  a515.64bLOG  aLogan, John David  aInvariant variational principles  aNew YorkbAcademic pressc1977  axv, 172p.b22 cm.cHB.  aMathematics in science and engineering seriesd138  aCalculus of variations