Citing Prover9 and Mace4

Please use something like this:

W. McCune, "Prover9 and Mace4", http://www.cs.unm.edu/~mccune/Prover9, 2005-2010.

Bibtex item:

@unpublished{ prover9-mace4,
    author = "W. McCune",
    title = "Prover9 and Mace4",
    note = "\verb|http://www.cs.unm.edu/~mccune/prover9/|",
    year = "2005--2010"}