JOURNAL OF DIFFERENTIAL EQUATIONS, vol. 81, no. 2, page. 255 - 274, 1989-10
COMMUNICATIONS IN MATHEMATICAL PHYSICS, vol. 121, no. 1, page. 11 - 33, 1989-03
COMMUNICATIONS IN PARTIAL DIFFERENTIAL EQUATIONS, vol. 14, no. 6, page. 833 - 834, 1989-01