Jiang Qian and Fan Wang. (2014). On the Approximation of the Derivatives of Spline Quasi-Interpolation in Cubic Spline $S_3^{1,2}(∆_{mn}^{(2)})$. Numerical Mathematics: Theory, Methods and Applications. 7 (1). 1-22. doi:10.4208/nmtma.2014.y12035