%0 Journal Article %A L. I. Kamynin %T A theorem on the internal derivative for a weakly degenerate second-order elliptic equation %J Sbornik. Mathematics %D 1986 %P 297-316 %V 54 %N 2 %U http://geodesic.mathdoc.fr/item/SM_1986_54_2_a1/ %G en %F SM_1986_54_2_a1