On a Problem of H. Brezis and F. Browder Concerning Sobolev Spaces Jean-Michel Coron Indiana University Mathematics Journal 1984 text pdf 10.1512/iumj.1984.33.33009 10.1512/iumj.1984.33.33009 en Indiana Univ. Math. J. 33 (1984) 179 - 183 state-of-the-art mathematics http://iumj.org/access/