1. Bandle, C. 1980. “Isoperimetric Inequalities and Applications”. Boston-London- Melburne: Pitman Publ.
2. Courant, R. and Hilbert, D. 1953. “Methods of Mathematical Physicss”. New York: John Wiley,
3. Hardy, G.H., Littlewood, J.E. and Pólya, G. 1967. “Inequalities”. Cambridge: Cambridge Univ.Press,