A Semigroup associated to a linear control system on a Lie group
  Let us consider a linear control system \Sigma on a connected Lie group G. It is known that the accessibility set A from the identity e is in general not a semigroup. In this article we associate a new algebraic object S to \Sigma which turns out to be a semigroup, allowing the use of the semigroup machinery to approach \Sigma. In particular, we obtain some controllability results. 
Victor Ayala and Adriano da Silva
math.DS