@article{GDZPPN00206457X, title = {A remark on two dimensional periodic potentials.}, journal = {Commentarii mathematici Helvetici}, volume = {57}, year = {1982}, pages = {130-134}, zbl = {0539.35059}, url = {http://dml.mathdoc.fr/item/GDZPPN00206457X} }
Trubowitz, E.; Dahlberg, B.E.J. A remark on two dimensional periodic potentials.. Commentarii mathematici Helvetici, Tome 57 (1982) pp. 130-134. http://gdmltest.u-ga.fr/item/GDZPPN00206457X/