Distributed and Lumped Networks R. Duffin Indiana University Mathematics Journal 1959 text pdf 10.1512/iumj.1959.8.58051 10.1512/iumj.1959.8.58051 en Indiana Univ. Math. J. 8 (1959) 793 - 826 state-of-the-art mathematics http://iumj.org/access/