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2. S. Helgason,Differential Geometry and Symmetric Spaces, Academic Press, New York, 1962.
3. C. Martin, Grassmann Manifolds and Global Properties of the Riccati Equation, Proceedings of 2nd International Symposium on the Operator Theory of Networks and Systems, August, 1977, Lubbock, Texas.
4. M. Shayman, Ph.D. dissertation, Harvard University, 1980.
5. C. Martin, Grassmann Manifolds, Riccati Equations, and Feedback Invariants of Linear Systems, In C. Byrnes and C. Martin (editors),Geometrical Methods for the Theory of Linear Systems, Reidel Publishing Co., Dordrecht, The Netherlands, 1980.