@incollection{MEM_2011_40_1_a18,
     author = {Popivanov, Nedyu and Popov, Todor and Scherer, Rudolf},
     title = {Singular {Solutions} with {Exponential} {Growth} for the {(3+1)-D} {Wave} {Equation}},
     booktitle = {},
     series = {Mathematics and Education in Mathematics},
     pages = {200--206},
     year = {2011},
     volume = {40},
     number = {1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/MEM_2011_40_1_a18/}
}