Coxeter defines other groups with anti-unitary constructions , for example these three . The first was discovered and drawn by Peter McMullen in 1966 . Coxeter defines other groups with anti-unitary constructions , for instance these three : the first was discovered and drawn by Peter McMullen in 1966 . Coxeter defines with other constructions anti-unitary groups , eg these three : the first was discovered and drawn by Peter McMullen in 1966 .