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A technique used by André (1887) to provide an elegant solution to the Ballot Problem (Hilton and Pederson 1991).
References
André, D.  ``Solution directe du problème résolu par M. Bertrand.''  Comptes Rendus Acad. Sci. Paris
  105, 436-437, 1887.
 
Comtet, L.  Advanced Combinatorics.  Dordrecht, Netherlands: Reidel, p. 22, 1974.
 
Hilton, P. and Pederson, J.  ``Catalan Numbers, Their Generalization, and Their Uses.''  Math. Intel. 13, 64-75, 1991.
 
Vardi, I.  Computational Recreations in Mathematica.  Reading, MA: Addison-Wesley, p. 185, 1991.