On Derivation Ranges Constantin ApostolJ. Stampfli Indiana University Mathematics Journal 1976 text pdf 10.1512/iumj.1976.25.25067 10.1512/iumj.1976.25.25067 en Indiana Univ. Math. J. 25 (1976) 857 - 869 state-of-the-art mathematics http://iumj.org/access/