Hello all, I've always been told to keep my corners firm when I play, and have been for the past 9 years that I've played the instrument. My questions is, what is the role of the corners? I always thought that they were more for control of what my lips are doing and the notes that come out, but the more I pay attention to it, I notice that the corners are working more to keep the air inside my mouth than anything else. Is this the purpose of why we keep our corners firm? if it is, it's never been explained to me that way, thanks a lot in advance!