@article{10_4153_CMB_1983_066_4,
     author = {Ortel, Marvin and Schneider, Walter},
     title = {Curvature of {Level} {Curves} of {Harmonic} {Functions}},
     journal = {Canadian mathematical bulletin},
     pages = {399--405},
     year = {1983},
     volume = {26},
     number = {4},
     doi = {10.4153/CMB-1983-066-4},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1983-066-4/}
}