%0 Journal Article
%A S. A. Popov
%T Knotting of contractible two-dimensional polyhedra in~$\mathbf R^4$
%J Sbornik. Mathematics
%D 1972
%P 333-341
%V 18
%N 2
%I mathdoc
%U http://geodesic.mathdoc.fr/item/SM_1972_18_2_a11/
%G en
%F SM_1972_18_2_a11