@article{MZ_1937__42_168721,
     author = {J., Ridder},
     title = {\"Uber die gegenseitigen {Beziehungen} einiger ?trigonometrischer},
     journal = {Mathematische Zeitschrift},
     pages = {322--336},
     publisher = {mathdoc},
     volume = {42},
     year = {1937},
     zbl = {63.0207.02},
     url = {http://geodesic.mathdoc.fr/item/MZ_1937__42_168721/}
}