Authors: Bronshtejn I. U., Kopanskij A. Ya.
Abstract
Finitely smooth normal forms of four-dimensional systems of differential equations in the vicinity of a hyperbolic singular
point are investigated by using the condition $\frak A (k)$ introduced earlier.
Institutul de Matematică Academia de Ştiinţe
str. Academiei 5, MD-2028 Chişinău, Moldova