**Invited Speakers**

Aldo de Luca (Università di Napoli)

*A palindromization map in free monoids.*

Roberto Gorrieri (Università di Bologna)

*On Petri Net semantics for Process Calculi*

**Abstract:**We illustrate the motivations for giving Petri net semantics to process calculi, as well as the seminal approach of Degano, De Nicola and Montanari (DDM) for CCS. We single out the pros and cons of the DDM technique and propose a new approach, called BG (after Nadia Busi) that solves some of the problems of their approach. The BG approach is also illustrated on the interesting case of the pi-calculus. Finally some remarks are given on a different approach proposed by Roland Meyer.

Fabrizio Luccio (Università di Pisa)

*Two algorithmic issues from a teacher's perspective*

**Abstract:**Taken from a teacher's experience, the following two issues are interesting examples of mixing (elementary) mathematics with algorithmic needs.

1. Solving recurrence relations is a basic tool for analyzing recursive algorithms. However, the classical presentation found in textbooks is somehow unsatisfactory, because the recurrences encountered in most pratical problems are either too easy or too difficult for applying the theory. We show that two simplified relations are the main ones worth being investigated, and prove very simple solutions in order Theta for them.

2. The generation of prime numbers is a basic problem, e.g. in cryptography. However, understanding the efficientary of the methods used requires knowing some of the properties of such numbers. One can go from Gauss hypothesis in the frequency of primes, to Riemann's zeta function, to the prime number theorem, and to the Miller-and-Rabin's randomized algorithm. All presented in an understandable form for CS students.