[1] A. Cumani, �On the canonical representation of homogeneous Markov processes modelling failure-time distributions,� Microelectronics and Reliability, vol. 22, pp. 583�602, 1982.

[2] A. Bobbio and A. Cumani. Modelling wear-out by multistate homogeneous Markov processes. In E. Lauger and J. Moltoft, editors, Reliability in Electrical and Electronic Components and Systems (Proceedings EUROCON 82), pages 101-106, North-Holland, 1982.

[3] A. Bobbio and A. Cumani. Modelling wear-out by multistate homogeneous Markov processes. Discrete state stochastic systems with phase type distributed transition times. In Proceedings AMSE International Conference on Modelling and Simulation, Vol. 1.1, pages 173-192, Athens, 1984.

[4] A. Cumani, �Esp - A package for the evaluation of stochastic Petri nets with phase-type distributed transition times ,� in Proceedings International Workshop Timed Petri Nets. Torino

(Italy): IEEE Computer Society Press no. 674, 1985, pp. 144�151.

[5]� M. Ajmone Marsan, G. Balbo, A. Bobbio, G. Chiola, G. Conte, and A. Cumani, �The effect of execution policies on the semantics and analysis of stochastic Petri nets,� IEEE Transactions on Software Engineering, vol. SE-15, pp. 832�846, 1989.

[6] A. Bobbio and M. Telek. Non-exponential stochastic Petri nets: An overview of methods and techniques.Computer Systems: Science & Engineering, 13:6, 339-351, 1998.

[7] D. Aldous and L. Shepp, �The least variable phase type distribution is Erlang,� Stochastic

Models, vol. 3, pp. 467�473, 1987.

[8] A. Bobbio, A. Horv�th, M. Scarpa and M. Telek. Acyclic Discrete Phase Type Distributions: Properties and a Parameter Estimation Algorithm. Performance Evaluation, 4:1-32, 2003.