%0 Journal Article
%A Lee, S. J.
%T Perturbation of Direct Sum Differential Operators
%J Canadian journal of mathematics
%D 1978
%P 600-630
%V 30
%N 3
%U http://geodesic.mathdoc.fr/articles/10.4153/CJM-1978-053-7/
%R 10.4153/CJM-1978-053-7
%F 10_4153_CJM_1978_053_7