@article{MZ_1918__1_167448,
     author = {G., Pick},
     title = {\"Uber positive harmonische {Funktionen}},
     journal = {Mathematische Zeitschrift},
     pages = {44--51},
     year = {1918},
     volume = {1},
     zbl = {46.0473.02},
     url = {http://geodesic.mathdoc.fr/item/MZ_1918__1_167448/}
}