sentences:  These groups are characterized by i) an "n"-fold proper rotation axis "C"n; ii) a mirror plane "σh" normal to "C"n. The "C"1"h" group is the same as the "C"s group in the nonaxial groups section.The pyramidal groups are denoted by "C"nv.These groups are characterized by i) an "n"-fold proper rotation axis "C"n; ii) "n" mirror planes "σv" which contain "C"n. The "C"1"v" group is the same as the "C"s group in the nonaxial groups section.