%0 Journal Article %A I. S. Kukles %A L. B. Persidskaya %T On extending Frommer's method of investigation of a~singular point to a~system of three differential equations %J Izvestiâ vysših učebnyh zavedenij. Matematika %D 1968 %P 44-54 %N 9 %I mathdoc %U http://geodesic.mathdoc.fr/item/IVM_1968_9_a5/ %G ru %F IVM_1968_9_a5