If and are normed spaces, they are isomorphic normed spaces if there exists a linear bijection such that and its inverse are continuous. If one of the two spaces or is complete (or reflexive, separable, etc.) then so is the other space. Two normed spaces and are isometrically isomorphic if in addition, is an isometry, i.e., for every in . The Banach–Mazur distance between two isomorphic but not isometric spaces and gives a measure of how much the two spaces and differ.