@incollection{Gehrke,
    doi = {10.1007/978-3-540-70583-3_21},
    url = {https://doi.org/10.1007%2F978-3-540-70583-3_21},
    publisher = {Springer Berlin Heidelberg},
    pages = {246--257},
    author = {Mai Gehrke and Serge Grigorieff and Jean-{\'{E}}ric Pin},
    title = {Duality and Equational Theory of Regular Languages},
    booktitle = {Automata, Languages and Programming}
}

@incollection{Gehrke, doi = {10.1007/978-3-540-70583-3_21}, url = {https://doi.org/10.1007%2F978-3-540-70583-3_21}, publisher = {Springer Berlin Heidelberg}, pages = {246--257}, author = {Mai Gehrke and Serge Grigorieff and Jean-{\'{E}}ric Pin}, title = {Duality and Equational Theory of Regular Languages}, booktitle = {Automata, Languages and Programming} }