Zhu, L., Giani, S., Houston, P., & Schötzau, D. (2011). Energy Norm A-Posteriori Error Estimation for hp-Adaptive Discontinuous Galerkin Methods for Elliptic Problems in Three Dimensions. Mathematical Models and Methods in Applied Sciences, 21(02), 267-306. https://doi.org/10.1142/s0218202511005052