@article{AM2_1976__14_136606,
     author = {Wolfgang Walter},
     title = {On a functional equation of {Bellman} in the theory of dynamic programming.},
     journal = {Aequationes mathematicae},
     pages = {435--444},
     publisher = {mathdoc},
     volume = {14},
     year = {1976},
     zbl = {0333.49033},
     url = {http://geodesic.mathdoc.fr/item/AM2_1976__14_136606/}
}