Kamal Aboul-Hosn Dexter Kozen Local variable scoping and Kleene algebra with tests. 3-17 2008 76 J. Log. Algebr. Program. 1 http://dx.doi.org/10.1016/j.jlap.2007.10.007 db/journals/jlp/jlp76.html#Aboul-HosnK08