Structure of A* A-AA* Heydar Radjavi Indiana University Mathematics Journal 1967 text pdf 10.1512/iumj.1967.16.16002 10.1512/iumj.1967.16.16002 en Indiana Univ. Math. J. 16 (1967) 19 - 26 state-of-the-art mathematics http://iumj.org/access/