sentences:  The groups were defined by Gilbert Baumslag and Donald Solitar in 1962 to provide examples of non-Hopfian groups.The groups contain residually finite groups, Hopfian groups that are not residually finite, and non-Hopfian groups.Define 
  
  The matrix group generated by and is a homomorphic image of , via the homomorphism induced by 
  
  It is worth noting that this will not, in general, be an isomorphism.