Over the years the slogan Define & Conquer emerged for MTV and came true several times in research as well as in teaching. Its background is on the one hand the principle "divide and conquer" (divide et impera) which is not only well-known in computer science. On the other hand, theoretical computer science as well as mathematics often uses proofs. The aim is to show that the underlying definitions the theory consists of, as well as the formal model underlying the reality via abstraction has sufficiently good properties to build meaningful und practically relevant theories upon it. Only the one to provide the right definitions is able to conquer reality .. in the case of MTV the reality of distributed systems.