1. Casti, J., Ljung, L.: Some new analytic and computational results for operator Riccati equations. SIAM J. Control13, 817–826 (1975).
2. Curtain, R. F.: The infinite-dimensional Riccati equation with applications to affine hereditary differential systems. SIAM J. Control13, 1130–1143 (1975).
3. Da Prato, G.: Equation d'évolution dans des algèbres d'opérateurs et application à des équations quasi-linéaires. J. Math. Pures et Appl..48, 59–107 (1969).
4. Gail, H.-P., Sedlmayr, E., Traving, G.: Non-LTE line formation in turbulent media. Astron & Astrophys.44, 421–429 (1975).
5. Hackbusch, W.: A numerical method for solving parabolic equations with opposite orientations, Part I: Description of the method. Report 77-6, Mathematisches Institut (Angewandte Mathematik), Universität zu Köln, 1977.