A very singular solution for the dual porous medium equation and the asymptotic behaviour of general solutions. Francisco Bernis; Josephus Hulshof — 1993 Journal für die reine und angewandte Mathematik
The dipole solution for the porous medium equation in several space dimensions Josephus Hulshof; Juan Luis Vazquez — 1993 Annali della Scuola Normale Superiore di Pisa - Classe di Scienze