A Renewal Theorem William FellerS. Orey Indiana University Mathematics Journal 1961 text pdf 10.1512/iumj.1961.10.10041 10.1512/iumj.1961.10.10041 en Indiana Univ. Math. J. 10 (1961) 619 - 624 state-of-the-art mathematics http://iumj.org/access/