@article{Kemp_1982,
    doi = {10.1016/0012-365x(82)90123-6},
    url = {https://doi.org/10.1016%2F0012-365x%2882%2990123-6},
    year = {1982},
    publisher = {Elsevier {BV}},
    volume = {40},
    number = {2-3},
    pages = {225--234},
    author = {R. Kemp},
    title = {On the number of words in the language $\lbrace$w {$\epsilon$} {$\sigma$}$\ast$ $\mid$ w = {wR}$\rbrace$2},
    journal = {Discrete Mathematics}
}

@article{Kemp_1982, doi = {10.1016/0012-365x(82)90123-6}, url = {https://doi.org/10.1016%2F0012-365x%2882%2990123-6}, year = {1982}, publisher = {Elsevier {BV}}, volume = {40}, number = {2-3}, pages = {225--234}, author = {R. Kemp}, title = {On the number of words in the language $\lbrace$w {$\epsilon$} {$\sigma$}$\ast$ $\mid$ w = {wR}$\rbrace$2}, journal = {Discrete Mathematics} }