@article{SMJ2_2013_39_3-4_a12,
     author = {Krastanov, M. I. and Ribarska, N. K.},
     title = {Viability and an {Olech} {Type} {Result}},
     journal = {Serdica Mathematical Journal},
     pages = {423--446},
     publisher = {mathdoc},
     volume = {39},
     number = {3-4},
     year = {2013},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SMJ2_2013_39_3-4_a12/}
}