@article{UFA_2018_10_4_a2,
     author = {L. G. Valiullina and Kh. K. Ishkin and R. I. Marvanov},
     title = {Spectral asymptotics  for  fourth order differential operator  with two turning points},
     journal = {Ufa mathematical journal},
     pages = {24--39},
     publisher = {mathdoc},
     volume = {10},
     number = {4},
     year = {2018},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/UFA_2018_10_4_a2/}
}