@article{Ringel_1965,
    doi = {10.1007/bf02996313},
    url = {https://doi.org/10.1007%2Fbf02996313},
    year = {1965},
    month = {dec},
    publisher = {Springer Science and Business Media {LLC}},
    volume = {29},
    number = {1-2},
    pages = {107--117},
    author = {Gerhard Ringel},
    title = {Ein Sechsfarbenproblem auf der Kugel},
    journal = {Abhandlungen aus dem Mathematischen Seminar der Universität Hamburg}
}

@article{Ringel_1965, doi = {10.1007/bf02996313}, url = {https://doi.org/10.1007%2Fbf02996313}, year = {1965}, month = {dec}, publisher = {Springer Science and Business Media {LLC}}, volume = {29}, number = {1-2}, pages = {107--117}, author = {Gerhard Ringel}, title = {Ein Sechsfarbenproblem auf der Kugel}, journal = {Abhandlungen aus dem Mathematischen Seminar der Universität Hamburg} }