Ⅰ. INTRODUCTIONConsider the differential operators■and(a<sub>jk</sub>)is a symmetric real matrix.L<sub>x</sub> is a second order homogeneous left invariant opera-
文摘Ⅰ. INTRODUCTIONConsider the differential operators■and(a<sub>jk</sub>)is a symmetric real matrix.L<sub>x</sub> is a second order homogeneous left invariant opera-
