1. Semigroups of Operators and Approximations;Butzer,1967
2. Linear hereditary differential systems and their control;Delfour,1973
3. Linear Operators, Parts 1;Dunford,1959
4. Linear Operators, Parts 2;Dunford,1963
5. Some remarks on complete controllability;Fattorini;SIAM J. Contr.,1966