The Superposition Principle and Diffraction in Angular Sectors Julius Kane Indiana University Mathematics Journal 1966 text pdf 10.1512/iumj.1966.15.15015 10.1512/iumj.1966.15.15015 en Indiana Univ. Math. J. 15 (1966) 207 - 219 state-of-the-art mathematics http://iumj.org/access/