[3] R. E. Kalman P. L. Falb M. A. Arbib: 
Topics in Mathematical System Theory. McGraw-Hill, 1969. 
MR 0255260 
[4] G. Ladas V. Lakshmikanthan: 
Differential Equations in Abstract Spaces. Academic Press 1972. 
MR 0460832 
[5] E. Kamen: 
On an algebraic theory of systems defined by convolution operators. Math. Systems Theory 9 (1975), 57-74. 
MR 0395953 | 
Zbl 0318.93003 
[6] F. M. Kirillova S. V. Čurakova: 
On the problem of controllability of linear systems with aftereffect. Div. Urav. 3 (1967), 436-445. 
MR 0211773 
[7] E. D. Sontag: 
On linear systems and noncommutative rings. Math. System Theory 9 (1975), 327-344. 
MR 0452844 
[8] E. D. Sontag: Linear systems over commutative rings: A survey. Ricerche di Automatica 7 (1976), 1-33.