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. Invariant imbedding, random walk and scattering, II: Discrete versions;Bellman;J. Math. and Mech.,1960
4. Invariant imbedding and neutron transport theory, II: Functional equations;Bellman;J. Math. and Mech.,1958
5. Invariant imbedding and neutron transport in a rod of changing length;Bellman,1960