# Right group

A semi-group which is right simple (cf. Simple semi-group) and satisfies the left cancellation law. Every right group is a completely-simple semi-group. The property that a semi-group $S$ is a right group is equivalent to any of the following conditions: a) $S$ is right simple and contains an idempotent element; b) $S$ is regular (cf. Regular semi-group) and satisfies the left cancellation law; c) $S$ can be partitioned into left ideals which are (necessarily isomorphic) groups; and d) $S$ is the direct product of a group and a right zero semi-group (cf. [[Idempotents, semi-group of]). The notion of a left group is similar to that of a right group. Only groups are simultaneously right groups and left groups. Every completely-simple semi-group can be partitioned into right (left) ideals which are (necessarily isomorphic) right (left) groups.