Sinisa Crvenkovic Igor Dolinka Zoltán Ésik The Variety of Kleene Algebras with Conversion is not Finitely Based. 235-245 2000 230 Theor. Comput. Sci. 1-2 db/journals/tcs/tcs230.html#CrvenkovicDE00 http://dx.doi.org/10.1016/S0304-3975(99)00079-1