Cross-bifix-free sets via Motzkin paths generation
  Cross-bifix-free sets are sets of words such that no prefix of any word is a sufix of any other word. In this paper, we introduce a general constructive method for the sets of cross-bifix-free q-ary words of fixed length. It enables us to determine a cross-bifix-free words subset which has the property to be non-expandable. 
Elena Barcucci, Stefano Bilotta, Elisa Pergola, Renzo Pinzani,   Jonathan Succi
math.CO