Acknowledgements

I’d like to thank prof. Aniello Cimitle and Gerardo Canfora for their helpful leading along the three years of my study, explaining me how to study, how to realize research, how to evaluate my work. I hope they give me the opportunity to follow their steps forever. I’d like to thank my father and my mother for staying at my side along all the way and giving me the suggestions and the strength to reach my final goal; they teach me to reject the fear to fall down, but to have ever the will to stand up and go on. I’d like to thank also Gioia for her understanding, patience and help during the harder moments of weakness. Without her smile nothing could be done. I’d like to thank also Gloria for being every time I needed to discuss with her. I’d like to thank prof. Mario Piattini, Felix Garcia, Marcela Genero for their fruitful collaboration. I appreciate them both on the human and on the professional side. The deep relationship linking me to them is based on pure esteem and respect. I’d like to thank prof. Giuseppe di Lucca and Emilio Bellini for their collaboration in the research