@article{702392,
     title = {Some features of the nodal recovery of gradients from finite element approximations which produces superconvergence},
     booktitle = {Equadiff 7},
     series = {GDML\_Books},
     publisher = {BSB B.G. Teubner Verlagsgesellschaft},
     address = {Leipzig},
     year = {1990},
     pages = {305-308},
     zbl = {0724.65101},
     url = {http://dml.mathdoc.fr/item/702392}
}

Whiteman, J. R.; Goodsell, G. Some features of the nodal recovery of gradients from finite element approximations which produces superconvergence, dans Equadiff 7, GDML_Books,  (1990), pp. 305-308. http://gdmltest.u-ga.fr/item/702392/