The definition of a group normally used in the classroom is that of a set of a finite or an infinite number of elements, for which an operation is defined, subject to the four conditions of closure, associativity, identity and inverse. The group is usually specified by giving its group table. However, this is not very practical for a finite group of large order and is never possible for an infinite group. Also, the group table often contains redundant information and so is not very efficient.