Maximal Smoothing Operators C. CalderonE. FabesN. Riviere Indiana University Mathematics Journal 1974 text pdf 10.1512/iumj.1974.23.23073 10.1512/iumj.1974.23.23073 en Indiana Univ. Math. J. 23 (1974) 889 - 898 state-of-the-art mathematics http://iumj.org/access/