... X, and• f + g ≤ f + g for all f, g ∈ X (triangle inequal ity).From the triangle inequality we also get the inverse triangle inequality(Problem 0.1)|f − g | ≤ f − g . (0.15)Once ... lawshowss(f, g) + s(f, h) = 2s(f, g + h2). (0.46)Now choosing h = 0 (and using s(f, 0) = 0) shows s(f, g) = 2s(f, g 2) andthus s(f, g) + s(f, h) = s(f, g + h). Furthermore, by induction we inferm2ns(f, ... that in infinite dimensional spaces different norms will giveraise to different convergent sequences! In fact, the key to solving prob-lems in infinite dimensional spaces is often finding the right...