So I always thought that the whole point of the flexibility studies in like the Arban's was to teach you how to do lip trills. Now I'm very much guessing it was more my ignorant self that thought that. So what do flexibility studies exactly do? How do you go about practicing them? Do I go for speed to start, or accuracy, or both? And what are the best ones to use, there is a lot in the Vizzutti book, or should I use the Arban's?