René Thiemann Hans Zantema Jürgen Giesl Peter Schneider-Kamp Adding constants to string rewriting. 27-38 2008 19 Appl. Algebra Eng. Commun. Comput. 1 http://dx.doi.org/10.1007/s00200-008-0060-6 db/journals/aaecc/aaecc19.html#ThiemannZGS08