1. Shuffle Factorization is Unique;J. Berstel;TCS,2002
2. On the Uniqueness of Shuffle on Words and Finite Languages;F. Biegler;TCS,2009
3. Shuffle Quotient and Decompositions;C. Câmpeanu,2001
4. Tight Lower Bound for the State Complexity of Shuffle of Regular Languages;C. Câmpeanu;J. of Autom., Lang., and Comb.,2002