@incollection{AST_1977__50__197_0,
     author = {Krych, Micha{\l}},
     title = {Two remarks on structural stability of plane dynamical systems},
     booktitle = {Syst\`emes dynamiques II - Varsovie},
     series = {Ast\'erisque},
     pages = {197--204},
     publisher = {Soci\'et\'e math\'ematique de France},
     number = {50},
     year = {1977},
     mrnumber = {501155},
     zbl = {0406.58021},
     language = {en},
     url = {http://www.numdam.org/item/AST_1977__50__197_0/}
}