1. A. F. Antippa and A. J. Phares, “The Linear Potential: An Exact Solution” (to be published).
2. N. Ya. Vilenkin,Combinatorics(Academic, New York, 1971), pp. 74–75 (postage problem), and pp. 135–39 (characteristic equation).
3. Wilfred Kaplan,Ordinary Differential Equations(Addison-Wesley, Reading, Mass., 1958), pp. 350–57.
4. Henceforth we will use the word “parts” instead of the technical word “classes,” used in combinatorics theory.
5. “Partitioning subinterval” is more expressive for our purpose than the word summond.