@article{Schaft_1986,
    doi = {10.1007/bf01704916},
    url = {https://doi.org/10.1007%2Fbf01704916},
    year = {1986},
    month = {dec},
    publisher = {Springer Science and Business Media {LLC}},
    volume = {19},
    number = {1},
    pages = {239--275},
    author = {A. J. Schaft},
    title = {On realization of nonlinear systems described by higher-order differential equations},
    journal = {Mathematical Systems Theory}
}

@article{Schaft_1986, doi = {10.1007/bf01704916}, url = {https://doi.org/10.1007%2Fbf01704916}, year = {1986}, month = {dec}, publisher = {Springer Science and Business Media {LLC}}, volume = {19}, number = {1}, pages = {239--275}, author = {A. J. Schaft}, title = {On realization of nonlinear systems described by higher-order differential equations}, journal = {Mathematical Systems Theory} }