@article{M2AN_1987__21_4_679_0,
     author = {Nakao, Mitsuhiro T.},
     title = {Superconvergence of the gradient of {Galerkin} approximations for elliptic problems},
     journal = {ESAIM: Mod\'elisation math\'ematique et analyse num\'erique},
     pages = {679--695},
     year = {1987},
     publisher = {AFCET - Gauthier-Villars},
     address = {Paris},
     volume = {21},
     number = {4},
     mrnumber = {921833},
     zbl = {0642.65073},
     language = {en},
     url = {https://www.numdam.org/item/M2AN_1987__21_4_679_0/}
}