1. Agmon, S., Lectures on Elliptic Boundary Value Problems. Princeton: Van Nostrand 1965.
2. Chandrasekhar, S., Hydrodynamic and Hydromagnetic Stability. Oxford: University Press 1961.
3. Dunford, N., & J. T. Schwartz, Linear Operators, Part I: General Theory. New York: Interscience 1958.
4. Joseph, D. D., On the stability of the Boussinesq equations. Arch. Rational Mech. Anal. 20, 59–71 (1965).
5. Keller, J. B., & S. Antman, Bifurcation Theory and Nonlinear Eigenvalue Problems. Benjamin 1969.