1. Diffuse reflection of light by a foggy medium;Ambarzumian;Doklady Akad. Nauk SSSR,1943
2. On the principle of invariant imbedding and propagation through inhomogeneous media;Bellman,1956
3. On the principle of invariant imbedding and diffuse reflection from cylindrical regions;Bellman,1957
4. Functional equations, wave propagation and invariant imbedding;Bellman;J. Math. and Mech.,1959
5. Functional equations in adaptive processes and random transmission;Bellman;Trans. 1959 International Symposium on Circuit and Information Theory, IRE Trans. on Circuit Theory,1959