For example, [2,2] and [2,2 ] are subgroups index 2 of [2,2], , and are represented as (or ) and (or ) with generators {01,2} and {0,12} respectively. Their common subgroup index 4 is [2,2 ], and is represented by (or ), with the double-open marking a shared node in the two alternations, and a single rotoreflection generator {012}.