@article{Feraud_1930,
    title = {On Birkhoff’s Pfaffian systems},
    volume = {32},
    issn = {1088-6850},
    url = {http://dx.doi.org/10.1090/s0002-9947-1930-1501563-5},
    doi = {10.1090/s0002-9947-1930-1501563-5},
    number = {4},
    journal = {Transactions of the American Mathematical Society},
    publisher = {American Mathematical Society (AMS)},
    author = {Feraud, Lucien},
    year = {1930},
    pages = {817–831},
    date-added = {2023-11-23 8:54:18 +0100}
}

@article{Feraud_1930, title = {On Birkhoff’s Pfaffian systems}, volume = {32}, issn = {1088-6850}, url = {http://dx.doi.org/10.1090/s0002-9947-1930-1501563-5}, doi = {10.1090/s0002-9947-1930-1501563-5}, number = {4}, journal = {Transactions of the American Mathematical Society}, publisher = {American Mathematical Society (AMS)}, author = {Feraud, Lucien}, year = {1930}, pages = {817–831}, date-added = {2023-11-23 8:54:18 +0100} }