[1] P. Blanchard, RL. Devaney, G.L Hall, Differential Equations, Brooks/Cole, Cengage Learning, 2011. ISBN-13:978-0-495-56198-9
[2] J.T. Sandefur, Discrete dynamical systems, Theory and Applications, Clarendon Press, Oxford, 1990. ISBN 0-19-853384-5