“Nodal $\mathcal{O}(h^4)$-Superconvergence in 3D by Averaging Piecewise Linear, Bilinear, and Trilinear FE Approximations”. Journal of Computational Mathematics, vol. 28, no. 1, Aug. 2018, pp. 1-10, https://doi.org/10.4208/jcm.2009.09-m1004.