1. Chen, CP, Cheung, WS: Wilker- and Huygens-type inequalities and solution to Oppenheim’s problem. Integral Transforms Spec. Funct. 23(5), 325-336 (2012)
2. Chen, CP: Sharp Wilker- and Huygens-type inequalities for inverse trigonometric and inverse hyperbolic functions. Integral Transforms Spec. Funct. 23(12), 865-873 (2012)
3. Qi, F, Zhang, SQ, Guo, BN: Sharpening and generalizations of Shafer’s inequality for the arctangent function. J. Inequal. Appl. 2009, Article ID 930294 (2009)
4. Chen, CP, Cheung, WS, Wang, W: On Shafer and Carlson inequalities. J. Inequal. Appl. 2011, Article ID 840206 (2011)
5. Chen, CP, Cheung, WS: Sharpness of Wilker and Huygens type inequalities. J. Inequal. Appl. 2012, Article ID 72 (2012)