1. Lecture Notes in Computer Science;A. Aristizábal,2011
2. Arkhangelskii, A.V., Pontryagin, L.S.: General Topology I. Springer (1990)
3. Baccelli, F., Cohen, G., Olsder, G., Quadrat, J.P.: Synchronization and Linearity: An Algebra for Discrete Event Systems. Wiley (1992)
4. Lecture Notes in Computer Science;S. Bistarelli,2008
5. Bistarelli, S., Gadducci, F.: Enhancing constraints manipulation in semiring-based formalisms. In: ECAI 2006. FAIA, vol. 141, pp. 63–67. IOS Press (2006)