To cite package ‘lfl’ in publications use:

  Burda M, Štěpnička M (2021). “lfl: An R package for linguistic fuzzy
  logic.” _Fuzzy Sets and Systems_. ISSN 0165-0114,
  doi:10.1016/j.fss.2021.07.007
  <https://doi.org/10.1016/j.fss.2021.07.007>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {lfl: An {R} package for linguistic fuzzy logic},
    author = {Michal Burda and Martin Štěpnička},
    journal = {Fuzzy Sets and Systems},
    year = {2021},
    issn = {0165-0114},
    doi = {10.1016/j.fss.2021.07.007},
  }