@article{JRAM_1992__424_153391,
     author = {Peter Sj\"ogren and M.A. Picardello},
     title = {Boundary behaviour of eigenfunctions of the {Laplacian} in a bi-tree.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {137--148},
     publisher = {mathdoc},
     volume = {424},
     year = {1992},
     zbl = {0734.31010},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1992__424_153391/}
}