To cite aylmer in publications use:

Luke J. West, Robin K. S. Hankin (2008). Exact Tests for Two-Way Contingency Tables with Structural Zeros. Journal of Statistical Software 28(11). URL http://www.jstatsoft.org/v28/i11/.

Corresponding BibTeX entry:

  @Article{,
    title = {Exact Tests for Two-Way Contingency Tables with Structural
      Zeros},
    author = {Luke J. West and Robin K. S. Hankin},
    journal = {Journal of Statistical Software},
    year = {2008},
    volume = {28},
    number = {11},
    url = {http://www.jstatsoft.org/v28/i11/},
  }