On a class of degenerate elliptic equations
Yoshiaki Hashimoto, Tadato Matsuzawa · Nagoya Mathematical Journal · 1974
We shall prove in Chapter I the hypoellipticity for a class of degenerate elliptic operators of higher order. Chapter II will be devoted to the consideration of the regularity at the boundary for the solutions of general boundary problems for the equations considered in Chapter I being restricted to the second order.