Some Combinatorial Operators in Language Theory
  Multitildes are regular operators that were introduced by Caron et al. in order to increase the number of Glushkov automata. In this paper, we study the family of the multitilde operators from an algebraic point of view using the notion of operad. This leads to a combinatorial description of already known results as well as new results on compositions, actions and enumerations. 
Jean-Gabriel Luque and Ludovic Mignot and Florent Nicart
cs.FL cs.DM math.CO