1. Aho, Alfred V. and Jeffrey D. Ullman.  Foundations of Computer Science: C Edition.  New York:  Computer Science Press, 1995.
  2. Appel, A. W. and G. J. Jacobson, The World's Fastest Scrabble Program, Communications of the ACM, 31(5) 572-578, 585 (1988).
  3. Jensen, Sik C.  Design and Implementation of Crossword Compilation Programs.  Imada:  Odense University Press, 1997.