Florent Nicart Jean-Marc Champarnaud Tibor Csáki Tamás Gaál André Kempe Labelling Multi-Tape Automata with Constrained Symbol Classes. 847-858 2007 18 Int. J. Found. Comput. Sci. 4 http://dx.doi.org/10.1142/S0129054107005017 db/journals/ijfcs/ijfcs18.html#NicartCCGK07