Then the Sn groups (n=even) are obtained. Naturally n must be even since S^nn=σ^h when n is odd and both Ch and σh exist independently. These groups (n = odd) are conventionally designated Cnh. Also, when n=2, the S2 group (remember S2=i) is conventionally called C2 If we add to a Cn group nσv (n odd) or n/2σv and n/2σd (n even) mirror planes,but no other rotation axes, then the Cnv group are generated. If to the elements of Cn we add a horizontal mirror plane, then we generate the Cnh groups. The product of C^n and σ^h also generate an Sn symmetry element and its associated operations.