To cite package 'FuzzyNumbers' in publications use:

Gagolewski M., Caha J. (2018). FuzzyNumbers Package: Tools to Deal with Fuzzy Numbers in R. http://FuzzyNumbers.rexamine.com/.

Corresponding BibTeX entry:

  @Manual{,
    title = {FuzzyNumbers Package: Tools to Deal with Fuzzy Numbers in
      R},
    author = {Marek Gagolewski and Jan Caha},
    year = {2018},
    url = {http://FuzzyNumbers.rexamine.com/},
  }