The Rank and Hanna Neumann Property of Some Submonoids of a Free Monoid
  This work aims at further investigations on the work of Giambruno and Restivo to find the rank of the intersection of two finitely generated submonoids of a free monoid. In this connection, we obtain the rank of a finitely generated submonoid of a free monoid that is accepted by semi-flower automaton with two bpi's. Further, when the product automaton of two deterministic semi-flower automata with a unique bpi is semi-flower with two bpi's, we obtain a sufficient condition on the product automaton in order to satisfy the Hanna Neumann property. 
Shubh Narayan Singh, K. V. Krishna
cs.FL math.RA