On the Differentiability of Weak Solutions of a Differential Equation in Banach Space M. CrandallA. Pazy Indiana University Mathematics Journal 1969 text pdf 10.1512/iumj.1969.18.18072 10.1512/iumj.1969.18.18072 en Indiana Univ. Math. J. 18 (1969) 1007 - 1016 state-of-the-art mathematics http://iumj.org/access/