1. R. E. Bellman, K. L. Cooke, R. E. Kalaba, and G. M. Wing, Existence and uniqueness theorems in invariant imbedding—I: Conservation principles, The RAND Corporation, RM-3611-ARPA, May, 1903
2. Modern Analytic and Computational Methods in Science and Mathematics, Vol. 2;Bellman, R. E.,1964
3. Invariant imbedding, conservation relations, and non-linear equations with two-point boundary values;Bellman, Richard;Proc. Nat. Acad. Sci. U.S.A.,1960