Sur Les Actions Symplectiques Quasi-Primitives
  A transitive smooth action of a connected Lie group G on a manifold M is called almost primitive (resp. primitive) if G doesn't contain any proper subgroup (resp. any proper normal subgroup) whose induced action on M is transitive as well. The aim of the present work is to investigate some combinatory properties of symplectic actions of completely solvable Lie groups. 
Michel Nguiffo Boyom