Spectral Theory of Operators of Hankel Type, I James Howland Indiana University Mathematics Journal 1992 text pdf 10.1512/iumj.1992.41.41022 10.1512/iumj.1992.41.41022 en Indiana Univ. Math. J. 41 (1992) 409 - 426 state-of-the-art mathematics http://iumj.org/access/