Nunes, Cláudia; Pacheco, António (1998) Parameter estimation in MMPPs Proceedings of the 2nd International Symposium on Semi-Markov Models: Theory and Applications - Compiègne, December 9-11, 1998. Included in the section "Statistical Estimation II".
M. Silva, Fábio (2015) On Combinatorial Monoids PhD thesis in Mathematics, Lismath PhD programme, Faculdade de Ciências da Universidade de Lisboa, Lisboa, Portugal.