Postprint version. Published in Journal of Integral Equations and Operator Theory, Volume 24, Issue 4, December 1, 1996, pages 379-421. Copyright © 1996 Springer. The original publication is available at http://dx.doi.org/10.1007/BF01191619.
NOTE: At the time of publication, the author Mark Stankus was not yet affiliated with Cal Poly.