An $L^\infty $ estimate and a superconvergence result for a Galerkin method for elliptic equations based on tensor products of piecewise polynomialsJim Jr. Douglas, Todd Dupont and Mary Fanett WheelerR.A.I.R.O. Analyse Numérique, 8 R2 (1974) 61-66DOI: https://doi.org/10.1051/m2an/197408R200611
