@article{IM_1979__51_142638,
     author = {Toshikazu Sunada},
     title = {Rigidity of {Certain} {Harmonic} {Mappings.}},
     journal = {Inventiones mathematicae},
     pages = {297--307},
     publisher = {mathdoc},
     volume = {51},
     year = {1979},
     zbl = {0418.31005},
     url = {http://geodesic.mathdoc.fr/item/IM_1979__51_142638/}
}