@article{702398,
     title = {On an internal approximation of a class of elliptic eigenvalue problems},
     booktitle = {Equadiff 7},
     series = {GDML\_Books},
     publisher = {BSB B.G. Teubner Verlagsgesellschaft},
     address = {Leipzig},
     year = {1990},
     pages = {301-304},
     zbl = {0780.65064},
     url = {http://dml.mathdoc.fr/item/702398}
}

Vanmaele, M.; van Keer, R. On an internal approximation of a class of elliptic eigenvalue problems, dans Equadiff 7, GDML_Books,  (1990), pp. 301-304. http://gdmltest.u-ga.fr/item/702398/