@article{MEM_2012_41_1_a15,
     author = {Hristov, Tsvetan and Popivanov, Nedyu and Schneider, Manfred},
     title = {Quasi-Regular {Solutions} for {3D} {Equations} of {Tricomi} and {Keldish} {Types}},
     journal = {Mathematics and Education in Mathematics},
     pages = {173--179},
     publisher = {mathdoc},
     volume = {41},
     number = {1},
     year = {2012},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/MEM_2012_41_1_a15/}
}