binary operator: left group action g.x
a.b = (a,b), where a is the group element and b is an element of the set. The type/description/label/name may be subscripted or denoted by function notation, as might be the group to which it belongs and/or the set upon which it acts (typically, the label should denote in the order: group, set, descriptor). See also: ma'e'o, zi'a'o, ru'ei