%0 Journal Article
%A G. J. Butler
%T The existence of periodic solutions of an autonomous second order non-linear differential equation
%J Annales Polonici Mathematici
%D 1974
%P 165-174
%V 30
%N 2
%I mathdoc
%U http://geodesic.mathdoc.fr/articles/10.4064/ap-30-2-165-174/
%R 10.4064/ap-30-2-165-174
%G en
%F 10_4064_ap_30_2_165_174