The spaces in examples 1.1, 1.2, and 1.3 are each linear spaces: there is an obviously defined way, in each case, of adding two points in the space to obtain a new one in the same space. In 1.1 if x and y E ~. then x + y is also in ~; in 1.2 we define (f + g)(x) = f(x) + g(x); and in 1.3 we define