Mapping Properties of the Radon Transform Daniel OberlinE. Stein Indiana University Mathematics Journal 1982 text pdf 10.1512/iumj.1982.31.31046 10.1512/iumj.1982.31.31046 en Indiana Univ. Math. J. 31 (1982) 641 - 650 state-of-the-art mathematics http://iumj.org/access/