@unpublished{PrenovTarkhanov2008,
  author  = {B. Prenov and Nikolai Nikolaevich Tarkhanov},
  title   = {Kernel spikes of singular problems},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprint},
  number    = {(2001) 36},
  year    = {2008},
}