Díez, P., Parés, N. . and Huerta, A. . (2004) “Accurate upper and lower error bounds by solving flux-free local problems in ‘stars’”, European Journal of Computational Mechanics, 13(5-7), pp. 497–507. Available at: https://journals.riverpublishers.com/index.php/EJCM/article/view/2301 (Accessed: 19 June 2026).