Hadamard Multipliers of Infinite Matrices William Ruckle Indiana University Mathematics Journal 1975 text pdf 10.1512/iumj.1975.24.24079 10.1512/iumj.1975.24.24079 en Indiana Univ. Math. J. 24 (1975) 949 - 957 state-of-the-art mathematics http://iumj.org/access/