Continuous Functions of Operators: A Functional Calculus Donald Hadwin Indiana University Mathematics Journal 1978 text pdf 10.1512/iumj.1978.27.27010 10.1512/iumj.1978.27.27010 en Indiana Univ. Math. J. 27 (1978) 113 - 125 state-of-the-art mathematics http://iumj.org/access/