1. Coq 8.5 beta release. https://coq.inria.fr/news/123.html . Accessed 20 Mar 2015
2. Coqoon home page. https://itu.dk/research/tomeso/coqoon/ . Accessed 19 Mar 2015
3. MIT proofs page. http://proofs.csail.mit.edu/ . Accessed 19 Mar 2015
4. Peacoq home page. http://goto.ucsd.edu/peacoq/ . Accessed 19 Mar 2015
5. Proof general. http://proofgeneral.inf.ed.ac.uk/ . Accessed 20 Mar 2015