Almost-Periodic Solutions of a Certain Abstract Differential Equation H. GunzlerS. Zaidman Indiana University Mathematics Journal 1970 text pdf 10.1512/iumj.1970.19.19015 10.1512/iumj.1970.19.19015 en Indiana Univ. Math. J. 19 (1970) 155 - 158 state-of-the-art mathematics http://iumj.org/access/