@article{Boasson_1973,
    doi = {10.1016/s0022-0000(73)80036-4},
    url = {https://doi.org/10.1016%2Fs0022-0000%2873%2980036-4},
    year = {1973},
    month = {dec},
    publisher = {Elsevier {BV}},
    volume = {7},
    number = {6},
    pages = {583--596},
    author = {L. Boasson},
    title = {Two iteration theorems for some families of languages},
    journal = {Journal of Computer and System Sciences}
}

@article{Boasson_1973, doi = {10.1016/s0022-0000(73)80036-4}, url = {https://doi.org/10.1016%2Fs0022-0000%2873%2980036-4}, year = {1973}, month = {dec}, publisher = {Elsevier {BV}}, volume = {7}, number = {6}, pages = {583--596}, author = {L. Boasson}, title = {Two iteration theorems for some families of languages}, journal = {Journal of Computer and System Sciences} }