# Reversible semi-group

A semi-group in which any two right principal ideals intersect is left reversible: $\forall a,b, \in S\ \exists x,y \in S \ :\ ax = by$. A commutative semi-group is reversible, as $ab=ba$. A semi-group which is reversible and obeys the cancellation law can be embedded in a group, cf Imbedding of semi-groups.