**The operator norm for dummies**

I eventually converted to LaTeX, a text I had hand written on the grass, one afternoon in a park, for a student. I wrote it because I just could not understand why there was this feeling among Masters students that finding the norm of a linear operator, often an operator between infinite dimensional normed spaces, was difficult. It's actually very easy if, first of all, you start from a sensible definition of the norm (and not that *thing* you often see in books and lecture notes), and realize that it will never be anything else than one of three cases (which case you are depends on the geometry of the space).