Ferguson, Brian S.; Lim, G. C. (1998). Introduction to Dynamic Economic Problems. Manchester: Manchester University Press. p. 162. ISBN 0-7190-4996-2. 0-7190-4996-2 ↩
Léonard, Daniel; Long, Ngo Van (1992). Optimal Control Theory and Static Optimization in Economics. New York: Cambridge University Press. p. 181. ISBN 0-521-33158-7. 0-521-33158-7 ↩