1. Die Grundlehren der mathematischen Wissenschaften, Band 60;Collatz, Lothar,1960
2. S. G. Mikhlin, Integral Equations, Macmillan, New York, 1957, pp. 19–21.
3. W. B. Morgan, "Theory of the annular airfoil and ducted propeller," Fourth Symposium on Naval Hydrodynamics, ACR-92, U. S. Government Printing Office, Washington, D. C., 1962, pp. 151–197.