The result of the quotient in (a) is the real hypersphere S defined by the equation | Z | = | Z 0 | + ... + | Z n | = 1. The quotient in (b) realizes CP = S / S, where S represents the group of rotations. This quotient is realized explicitly by the famous Hopf fibration S → S → CP, the fibers of which are among the great circles of S 2 n + 1 .