Acknowledgements
I will be a little unconventional and reserve the first place to thank others than my supervisor. I would like to address the first acknowledgements to four persons that made it possible for me to actually start my doctoral education.
First of all, I would like to thank Carlos Ferrari. He is a remarkable person with very high humanitarian standards. Carlos is one of the closest friends of my father and transitively, a friend of mine. He is responsible in many ways for me taking up doctoral studies, but this is just a small part of the benefit of his friendship.
Javier Blanco introduced me to the scientific ideas of correctness, semantics, formal reasoning, to mention but a few of the important keywords of the subject of this dissertation. Later, he was my bridge over the Atlantic ocean, responsible for my introduction to the Dutch scientific environment. And he has been a great companion, too.
It took me a while to graduate from the University of La Plata. It was Juan Echagüe who made me do it. That was the moment we built our friendship. He was very supportive when I made the decision to do a PhD abroad. I learned from him how to confront such a big decision not only in the academic aspects but, more important, in my personal life.
During the last three months of 1994, I had the pleasure of visiting the Formal Methods Group at the Eindhoven University of Technology. It was there where I met Jos Baeten and had the chance to work with him and his people. Afterwards, Jos signed a big recommendation letter for the position I held during the past four years at Twente.
It has been a great pleasure to have Ed Brinksma as my supervisor. He had the big challenge to confront my stubbornness, which, by the way, is not an easy task. At the same time, Ed has always been supportive and encouraging concerning my work and career and I learned a big deal from him. I wonder if I could have had a better supervisor.
I have been delighted to work with Joost-Pieter Katoen. 
and the stochastic automata model were born after a remark of him in the corridor. Thereafter, we have not stopped working and creating new ideas on the subject. Both Ed and Joost-Pieter reviewed the manuscript draft before it was submitted. Their suggestions and comments helped to improve considerably this dissertation, specially in the presentation aspects.
Apart from Ed and Joost-Pieter, the other members of the Graduation Committee are Frits Vaandrager, Jos Baeten, Wang Yi, Boudewijn Haverkort, Ignas Niemegeers, and the Chairman, Peter Apers. I am grateful to them for accepting the (literally) heavy task of going through my dissertation. In particular Jos and Frits made several remarks that helped me to correct mistakes that, though they might not seem very important, they could have annoyed or misled the reader. In this respect, Mariëlle Stoelinga is also acknowledges. She spotted a mistake that would have affected the quality of the thesis.
Since the first day, I enjoyed going to work every day. The Formal Methods and Tools group at the University of Twente is simply uncommon. You can rarely see such an enjoyable group of smart and kind people fitting together so well. I would like to acknowledge the friendship of Theo Ruys and Lex Heerink. Theo went through the adventure of sharing an office with me since he came. No better fellow could I have had as an officemate. Lex had the challenging task of making this foreign guy feel comfortable in his land. He certainly did. Holger Hermanns, Rom Langerak, Pim Kars, and Dino Distefano have also been marvelous companions. Holger has also contributed with technical discussions that have influenced the contents of this dissertation. Arend Rensink gave helpful answers to my questions and provided great conversations. Jan Tretmans has been quite helpful when I just arrive to Enschede. I also would like to thank Albert, Axel, Han, Henk, Jan F., and René. And Joke Lammerink, of course, always there to take care of all these things I cannot do very well.
I have learned a lot working and coauthoring with other people. Many of them, I have already mentioned. There are still a few to whom I am also entirely grateful. They are Jan Springintveld, Frits Vaandrager, Chris Verhoef, and Sjouke Mauw.
I am also grateful to many people at the ex-TIOS and CTIT, in particular, Marloes Castañeda and Ila Reinders; colleagues and friends at the PROMISE group and at the IPA school; people at InCo, Montevideo, in particular, Alfredo Olivero and Luis Sierra; people at DoCS, Uppsala, in particular, Wang Yi and Justin Pearson. I should also acknowledge that it was in Uppsala where I started to write my thesis. I also want to thank my friends and colleagues at the Computer Science Department in La Plata (now, Faculty of Informatics), in particular, Armando De Giusti, Gabriel Baum, and Gustavo Rossi. I have also enjoyed my short visits to the University of Erlangen Nürnberg, Verimag (Grenoble), and IRISA (Rennes); I would like to acknowledge the hospitality of Ulrich Herzog, Sergio Yovine, and Sophie Pinchinat.
In this job, one has the chance to meet a lot of nice people at conferences, schools, and other kind of meetings. It is unavoidable to learn from them things that range from science to social behaviour. I would like to mention a few whose influence was deeper and I have not yet mentioned. They are Christel Baier, Dimitra Giannakopoulou, and Roberto Segala. The list grows immensely large. If you had the chance to have a glass of wine, beer, or soft drink with me during these events, you are certainly acknowledged here.
A big thanks to my friends that make my life interesting in The Netherlands. To name a few: Paula, Aljosa, Anna, Susana, Ciro, Sonia, Val, and Lyande.
Y por supuesto, todos mis amigos en la Argentina que siempre me han apoyado: Gabriel, Cecilia, Mariel, Fabián, mis viejos amigos, los de la facu, y los más nuevos también.
Un "muchas gracias" con un beso grande y un fuerte abrazo a mi papá, mi mamá, Laura, Nacho, Paula, Coqui, Uli, Manu, mi tía Inés, y el resto de la familia.
Enschede, 1999
Pedro R. D'Argenio