COMMUNICATIONS IN PARTIAL DIFFERENTIAL EQUATIONS, vol. 14, no. 6, page. 833 - 834, 1989-01
COMMUNICATIONS IN PARTIAL DIFFERENTIAL EQUATIONS, vol. 13, no. 12, page. 1499 - 1519, 1988-02
LETTERS IN MATHEMATICAL PHYSICS, vol. 12, no. 2, page. 87 - 91, 1986-08