@article{Sauer_1972,
    doi = {10.1016/0097-3165(72)90019-2},
    url = {https://doi.org/10.1016%2F0097-3165%2872%2990019-2},
    year = {1972},
    month = {jul},
    publisher = {Elsevier {BV}},
    volume = {13},
    number = {1},
    pages = {145--147},
    author = {N Sauer},
    title = {On the density of families of sets},
    journal = {Journal of Combinatorial Theory, Series A}
}

@article{Sauer_1972, doi = {10.1016/0097-3165(72)90019-2}, url = {https://doi.org/10.1016%2F0097-3165%2872%2990019-2}, year = {1972}, month = {jul}, publisher = {Elsevier {BV}}, volume = {13}, number = {1}, pages = {145--147}, author = {N Sauer}, title = {On the density of families of sets}, journal = {Journal of Combinatorial Theory, Series A} }