@unpublished{ShlapunovTarkhanov2012,
  author  = {Alexander Shlapunov and Nikolai Nikolaevich Tarkhanov},
  title   = {On completeness of root functions of Sturm-Liouville problems with discontinuous boundary operators},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprints des Instituts f{\"u}r Mathematik der Universit{\"a}t Potsdam},
  number    = {1(2012)11},
  year    = {2012},
}