Almeida Pereira, Orlando J. B., and Jose P. Moitinho de Almeida. “Adaptive Refinement for a Local Error Bound Based on Duality”. Computer Assisted Methods in Engineering and Science, vol. 10, no. 4, Jan. 2023, pp. 565-74, https://cames3.ippt.pan.pl/index.php/cames/article/view/1065.