[6] Buzano, M. L.: 
Generalizzazione della diseguaglianza di Cauchy-Schwarz. Rend. Semin. Mat., Torino Italian 31 (1974), 405-409. 
MR 0344857 | 
Zbl 0285.46016[7] Dragomir, S. S.: 
Some refinements of Schwartz inequality. Proceedings of the Symposium of Mathematics and Its Applications Timişoara Research Centre of the Romanian Academy, Timişoara (1986), 13-16. 
Zbl 0594.46018[8] Dragomir, S. S.: 
Power inequalities for the numerical radius of a product of two operators in Hilbert spaces. Sarajevo J. Math. 5 (2009), 269-278. 
MR 2567758 | 
Zbl 1225.47008[17] Pečarić, J., Furuta, T., Hot, J. Mićić, Seo, Y.: 
Mond-Pečarić Method in Operator Inequalities: Inequalities for Bounded Selfadjoint Operators on a Hilbert Space. Monographs in Inequalities 1. Element, Zagreb (2005). 
MR 3026316 | 
Zbl 1135.47012