Toeplitz operators on noncommutative spheres and an index theorem T. NatsumeC. Olsen Toeplitz operatorsC* algebra Indiana University Mathematics Journal 1997 text pdf 10.1512/iumj.1997.46.1152 10.1512/iumj.1997.46.1152 en Indiana Univ. Math. J. 46 (1997) 1055 - 1112 state-of-the-art mathematics http://iumj.org/access/