%0 Journal Article %A M. N. Yakovlev %T Existence of $2^n$ periodic solutions of a system of $n$ differential equations of first order %J Zapiski Nauchnykh Seminarov POMI %D 2002 %P 247-262 %V 284 %U http://geodesic.mathdoc.fr/item/ZNSL_2002_284_a12/ %G ru %F ZNSL_2002_284_a12