@article{Gessel_1980,
    doi = {10.1016/0097-3165(80)90074-6},
    url = {https://doi.org/10.1016%2F0097-3165%2880%2990074-6},
    year = {1980},
    month = {may},
    publisher = {Elsevier {BV}},
    volume = {28},
    number = {3},
    pages = {321--337},
    author = {Ira M Gessel},
    title = {A factorization for formal laurent series and lattice path enumeration},
    journal = {Journal of Combinatorial Theory, Series A}
}

@article{Gessel_1980, doi = {10.1016/0097-3165(80)90074-6}, url = {https://doi.org/10.1016%2F0097-3165%2880%2990074-6}, year = {1980}, month = {may}, publisher = {Elsevier {BV}}, volume = {28}, number = {3}, pages = {321--337}, author = {Ira M Gessel}, title = {A factorization for formal laurent series and lattice path enumeration}, journal = {Journal of Combinatorial Theory, Series A} }