Because C ^n and ^sh commute we have ^Sn = C ^ n^sh for the general rotoreflection operation. Since ^shn = E ^ for even m and for m odd ^shm = ^sh, an Sn axis requires simultaneous independent existence of a Cn/2 rotation axis and an inversion center when n is even. For example, an S6 axis generates the operations for the point group S6. They are shown below.