@article{MM2_1970__3_154026,
     author = {Rainer Walden and Wilhelm Vortisch},
     title = {Ein {Kongruenzsatz} f\"ur {Eifl\"achen.}},
     journal = {Manuscripta mathematica},
     pages = {315--320},
     publisher = {mathdoc},
     volume = {3},
     year = {1970},
     zbl = {0201.24204},
     url = {http://geodesic.mathdoc.fr/item/MM2_1970__3_154026/}
}