%0 Journal Article
%A Pressman, Irwin S.
%T Obstructions to Liftings in Commutative Squares
%J Canadian journal of mathematics
%D 1971
%P 977-982
%V 23
%N 6
%U http://geodesic.mathdoc.fr/articles/10.4153/CJM-1971-105-2/
%R 10.4153/CJM-1971-105-2
%F 10_4153_CJM_1971_105_2