@incollection{Flajolet_1974,
    doi = {10.1007/978-3-662-21545-6_34},
    url = {https://doi.org/10.1007%2F978-3-662-21545-6_34},
    year = {1974},
    publisher = {Springer Berlin Heidelberg},
    pages = {446--457},
    author = {P. Flajolet and J. M. Steyaert},
    title = {On Sets Having Only Hard Subsets},
    booktitle = {Automata, Languages and Programming}
}

@incollection{Flajolet_1974, doi = {10.1007/978-3-662-21545-6_34}, url = {https://doi.org/10.1007%2F978-3-662-21545-6_34}, year = {1974}, publisher = {Springer Berlin Heidelberg}, pages = {446--457}, author = {P. Flajolet and J. M. Steyaert}, title = {On Sets Having Only Hard Subsets}, booktitle = {Automata, Languages and Programming} }