The generalized Szendrei expansion of an R-unipotent semigroup
          Branco, Mário J. J.; Gomes, Gracinda M. S.  
          
          Acta Mathematica Hungarica, 123(1-2) (2009), 11-26  
          http://dx.doi.org/10.1007/s10474-009-8025-1  
           
          The generalized Szendrei expansion S Pr is defined for an 
 R-unipotent semigroup S and the projection of S Pr onto S is proved to be an initial object in the category of all F-morphisms onto S. Also, the languages recognized by these expansions are described following the semidirect product principle.   
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