To cite package ‘set6’ in publications use:

  Sonabend R, Kiraly F (2020). “set6: R6 Mathematical Sets Interface.”
  _Journal of Open Source Software_. doi:10.21105/joss.02598
  <https://doi.org/10.21105/joss.02598>.
  <https://joss.theoj.org/papers/10.21105/joss.02598>.

A BibTeX entry for LaTeX users is

  @Article{set6,
    title = {set6: R6 Mathematical Sets Interface},
    author = {Raphael Sonabend and Franz J. Kiraly},
    journal = {Journal of Open Source Software},
    year = {2020},
    month = {nov},
    doi = {10.21105/joss.02598},
    url = {https://joss.theoj.org/papers/10.21105/joss.02598},
  }