To cite sets in publications use:

Meyer D and Hornik K (2009). “Generalized and Customizable Sets in R.” Journal of Statistical Software, 31(2), pp. 1–27. doi: 10.18637/jss.v031.i02.

Corresponding BibTeX entry:

  @Article{,
    title = {Generalized and Customizable Sets in {R}},
    author = {David Meyer and Kurt Hornik},
    journal = {Journal of Statistical Software},
    year = {2009},
    volume = {31},
    number = {2},
    pages = {1--27},
    doi = {10.18637/jss.v031.i02},
  }