1. I. H. Shames,Mechanics of Fluids, McGraw-Hill, New York, 1962, pp. 109, 162.
2. W. Kaplan,Advanced Calculus, Addison-Wesley, Reading, MA, 1973, p. 337.
3. R. Weinstock,Calculus of Variations, Dover, New York, 1974, p. 16.
4. H. Lamb,Hydrodynamics, 6th ed., Dover, New York, 1945, pp. 12, 21, 22.
5. R. Courant and D. Hilbert,Methods of Mathematical Physics, Vol. 1, Interscience, New York, 1953, pp. 112, 185.