Liesbeth De Mol. Study of Limits of Solvability in Tag Systems. In Jérôme Olivier Durand-Lose, Maurice Margenstern, editors, Machines, Computations, and Universality, 5th International Conference, MCU 2007, Orléans, France, September 10-13, 2007, Proceedings. Volume 4664 of Lecture Notes in Computer Science, pages 170-181, Springer, 2007. [doi]