Analytic Functions and Hypergroups of Function Pairs Kenneth Stephenson Indiana University Mathematics Journal 1982 text pdf 10.1512/iumj.1982.31.31059 10.1512/iumj.1982.31.31059 en Indiana Univ. Math. J. 31 (1982) 843 - 884 state-of-the-art mathematics http://iumj.org/access/