On the Spectrum of a Class of Toeplitz Operators R. Douglas Indiana University Mathematics Journal 1969 text pdf 10.1512/iumj.1969.18.18034 10.1512/iumj.1969.18.18034 en Indiana Univ. Math. J. 18 (1969) 433 - 435 state-of-the-art mathematics http://iumj.org/access/