@article{Oppen_1980,
    doi = {10.1145/322203.322204},
    url = {https://doi.org/10.1145%2F322203.322204},
    year = {1980},
    month = {jul},
    publisher = {Association for Computing Machinery ({ACM})},
    volume = {27},
    number = {3},
    pages = {403--411},
    author = {Derek C. Oppen},
    title = {Reasoning About Recursively Defined Data Structures},
    journal = {Journal of the {ACM}}
}

@article{Oppen_1980, doi = {10.1145/322203.322204}, url = {https://doi.org/10.1145%2F322203.322204}, year = {1980}, month = {jul}, publisher = {Association for Computing Machinery ({ACM})}, volume = {27}, number = {3}, pages = {403--411}, author = {Derek C. Oppen}, title = {Reasoning About Recursively Defined Data Structures}, journal = {Journal of the {ACM}} }