1. Beckenbach, E. F. andBellman, R.,Inequalities. Springer-Verlag, New York, 1965.
2. Cheung, W. S.,On Poincaré type integral inequalities. Proc. Amer. Math. Soc.119 (1993), 857–863.
3. Cheung, W. S.,Opial-type inequalities with m functions in n variables. Mathematika39 (1992), 319–326.
4. Friedman, A.,Partial differential equations of parabolic type. Prentice-Hall, Englewood Cliffs, NY, 1964.
5. Hardy, G. H., Littlewood, J. E. andPólya, G.,Inequalities. Cambridge Univ. Press, Cambridge, 1952.