@incollection{Niwi_ski_1998,
    doi = {10.1007/bfb0028571},
    url = {https://doi.org/10.1007%2Fbfb0028571},
    year = {1998},
    publisher = {Springer Berlin Heidelberg},
    pages = {320--331},
    author = {Damian Niwi{\'{n}}ski and Igor Walukiewicz},
    title = {Relating hierarchies of word and tree automata},
    booktitle = {{STACS} 98}
}

@incollection{Niwi_ski_1998, doi = {10.1007/bfb0028571}, url = {https://doi.org/10.1007%2Fbfb0028571}, year = {1998}, publisher = {Springer Berlin Heidelberg}, pages = {320--331}, author = {Damian Niwi{\'{n}}ski and Igor Walukiewicz}, title = {Relating hierarchies of word and tree automata}, booktitle = {{STACS} 98} }