▁ ▁Sum mary ▁ ▁This ▁is ▁a ▁summary ▁of ▁ 4 - dimensional ▁point ▁groups ▁in ▁C ox eter ▁notation . ▁ 2 2 7 ▁of ▁them ▁are ▁cry stal log raph ic ▁point ▁groups ▁( for ▁particular ▁values ▁of ▁p ▁and ▁q ). ▁( nc ) ▁is ▁given ▁for ▁non - c ry stal log raph ic ▁groups . ▁Some ▁cry stal log raph ic ▁group ▁have ▁their ▁orders ▁indexed ▁ ▁( order . index ) ▁by ▁their ▁abstract ▁group ▁structure . ▁ ▁See ▁also ▁▁ ▁Point ▁group ▁ ▁Point ▁groups ▁in ▁two ▁dimensions ▁ ▁Point ▁groups ▁in ▁three ▁dimensions ▁ ▁References ▁▁▁ ▁H . S . M . ▁C ox eter , ▁Reg ular ▁Poly top es , ▁ 3 rd ▁Edition , ▁D over ▁New ▁York , ▁ 1 9 7 3 ▁▁ ▁K ale idos cop es : ▁Selected ▁Writ ings ▁of ▁H . S . M . ▁C ox eter , ▁edited ▁by ▁F . ▁Arthur ▁Sh erk , ▁Peter ▁Mc M ull en , ▁Anthony ▁C . ▁Thompson , ▁Asia ▁I vic ▁We iss , ▁W iley - In ters cience ▁Public ation , ▁ 1 9 9 5 , ▁▁ ▁( P aper ▁ 2 2 ) ▁H . S . M . ▁C ox eter , ▁Reg ular ▁and ▁Sem i ▁Reg ular ▁Poly top es ▁I , ▁[ Math . ▁Zeit . ▁ 4 6 ▁( 1 9 4 0 ) ▁ 3 8 0 – 4 0 7 , ▁MR ▁ 2 ,