For example, [4,4] has three independent nodes in the Coxeter diagram when the 4 s are removed, so its commutator subgroup is index 2, and can have different representations, all with three operators: [4,4 ], [1,4,1,4,1 ], [1,4,4,1 ], or [(4,4,2)]. A general notation can be used with + c as a group exponent, like [4,4].