To cite package 'FuzzyNumbers' in publications use:

Gagolewski M. (2012). FuzzyNumbers Package: Tools to deal with fuzzy numbers in R. http://www.ibspan.waw.pl/~gagolews/FuzzyNumbers.

Corresponding BibTeX entry:

  @Manual{,
    title = {FuzzyNumbers Package: Tools to deal with fuzzy numbers in
      R},
    author = {Marek Gagolewski},
    year = {2012},
    url = {http://www.ibspan.waw.pl/~gagolews/FuzzyNumbers/},
  }