@article{Mortimer:MLQ:1975,
    doi = {10.1002/malq.19750210118},
    url = {https://doi.org/10.1002%2Fmalq.19750210118},
    year = {1975},
    month = {jan},
    publisher = {Wiley},
    volume = {21},
    number = {1},
    pages = {135--140},
    author = {Michael Mortimer},
    title = {On languages with two variables},
    journal = {Mathematical Logic Quarterly}
}

@article{Mortimer:MLQ:1975, doi = {10.1002/malq.19750210118}, url = {https://doi.org/10.1002%2Fmalq.19750210118}, year = {1975}, month = {jan}, publisher = {Wiley}, volume = {21}, number = {1}, pages = {135--140}, author = {Michael Mortimer}, title = {On languages with two variables}, journal = {Mathematical Logic Quarterly} }