@article{AM2_1978__17_136716,
     author = {Richard Bellman and E. Stanley Lee},
     title = {Functional equations in dynamic programming.},
     journal = {Aequationes mathematicae},
     pages = {1--18},
     year = {1978},
     volume = {17},
     zbl = {0397.39016},
     url = {http://geodesic.mathdoc.fr/item/AM2_1978__17_136716/}
}