Absolute Convergence and Integrability of Trigonometric Series R. Boas, Jr. Indiana University Mathematics Journal 1956 text pdf 10.1512/iumj.1956.5.55020 10.1512/iumj.1956.5.55020 en Indiana Univ. Math. J. 5 (1956) 621 - 632 state-of-the-art mathematics http://iumj.org/access/