References
- Starling , S. G. and Woodall , A. J. 1952 . Physics , 3 4 London : Longmans, Green & Co. .
- Knopp , K. 1952 . Elements of the Theory of Functions 113 – 115 . Dover
- Courant , R. 1956 . Differential and Integral Calculus , Vol. I , 372 – 375 . Blackie & Son .