Calculus of Set Valued Functions and Control Henry Hermes Indiana University Mathematics Journal 1969 text pdf 10.1512/iumj.1969.18.18006 10.1512/iumj.1969.18.18006 en Indiana Univ. Math. J. 18 (1969) 47 - 59 state-of-the-art mathematics http://iumj.org/access/