1. P. Duwez and H. E. Martens, “The powder metallurgy of porous metals and alloys having a controlled porosity,” AIME Tech. Pub. No. 2343, 1948.
2. E. G. C. Poole,Introduction of the Theory of Linear Differential Equations(Clarendon Press, Oxford, 1936), p. 139.
3. Reference 2, p. 140.
4. E. T. Whittaker and G. N. Watson,A Course of Modern Analysis(University Press, Cambridge, 1920), p. 275.
5. E. Jahnke and F. Emde,Tables of Functions(Dover Publications, New York, 1943), p. 275.