1. IJ.J.Aalbersberg, G.Rozenberg, Theory of traces, tec. Rep. 86-16, Inst. of Appl.Math. and Comp. Sci. University of Leiden, 1986
2. IJ.J. Aalbersberg, H.J. Hogeboom, Decision problems for regular trace languages, Proc. 14th ICALP, Lect.Not.Comp.Sci. 267, 251–259, Springer, 1987
3. A. Bertoni, M. Brambilla, G. Mauri, N. Sabadini, An application of the theory of free partially commutative monoids: asymptotic densities of trace languages, Lect. Not. Comp. Sci. 118, 205–215, Springer, 1981
4. A. Bertoni, G. Mauri, N. Sabadini, Unambiguous regular trace languages. Algebra Combinatorics and Logica in Computer Science, Colloquia Mathematica Societatis J. Bolyai, vol.42, 113–123, North Holland, Amsterdam 1985
5. D. Bruschi, G. Pighizzini, N. Sabadini, On the existence of the minimum asynchronous automaton and on decision problems for unambiguous regular trace languages, Proc. STACS 88, Lect.Notes Comp.Sci. 294, pp.334–346, Springer, 1988