@article{DE_1985_21_11_a2,
     author = {\`E. I. Grudo},
     title = {Bifurcation equations for the existence of periodic solutions of periodic {Pfaffian} systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1857--1867},
     publisher = {mathdoc},
     volume = {21},
     number = {11},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1985_21_11_a2/}
}