Algebaic Theory of Fredholm Operators Lewis CoburnA. Lebow Indiana University Mathematics Journal 1966 text pdf 10.1512/iumj.1966.15.15037 10.1512/iumj.1966.15.15037 en Indiana Univ. Math. J. 15 (1966) 577 - 584 state-of-the-art mathematics http://iumj.org/access/