To cite package 'FuzzyNumbers' in publications use:

Gagolewski M, Caha J (2021). FuzzyNumbers Package: Tools to Deal with Fuzzy Numbers in R. https://github.com/gagolews/FuzzyNumbers/.

Corresponding BibTeX entry:

  @Manual{,
    title = {FuzzyNumbers Package: Tools to Deal with Fuzzy Numbers in
      R},
    author = {Marek Gagolewski and Jan Caha},
    year = {2021},
    url = {https://github.com/gagolews/FuzzyNumbers/},
  }