@unpublished{YagdjianGalstian2009,
  author  = {Karen Yagdjian and Anahit Galstian},
  title   = {Fundamental solutions for wave equation in de Sitter model of universe},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprint},
  number    = {(2007) 06},
  year    = {2009},
}