@article{JDM_1919__28_145558,
     author = {K. Bopp},
     title = {Der {Modularkreis} der {Ellipse.}},
     journal = {Jahresbericht der Deutschen Mathematiker-Vereinigung},
     pages = {20--25},
     publisher = {mathdoc},
     volume = {28},
     year = {1919},
     zbl = {47.0361.03},
     url = {http://geodesic.mathdoc.fr/item/JDM_1919__28_145558/}
}