1. Braess, D.: Finite elements. Theory, Fast Solvers, and Applications in Solid Mechanics, 2nd edn., pp. xviii+352. Translated from the 1992 German edition by Larry L. Schumaker. Cambridge University Press, Cambridge (2001)
2. Buzano, M.L.: Generalizzazione della disiguaglianza di Cauchy-Schwaz (Italian). Rend. Sem. Mat. Univ. e Politech. Torino 31 (1971/73), 405–409 (1974)
3. Diaz, J.B., Metcalf, F.T.: Complementary inequalities. III. Inequalities complementary to Schwarz’s inequality in Hilbert space. Math. Ann. 162, 120–139 (1965/1966)
4. Dragomir, S.S.: Some refinements of Schwarz inequality, Simposional de Matematică şi Aplicaţii, Polytechnical Institute Timişoara, Romania, 1–2 Nov 1985, 13–16. ZBL 0594:46018.
5. Dragomir, S.S.: A generalisation of Grüss’ inequality in inner product spaces and applications. J. Math. Anal. Appl. 237, 74–82 (1999)