A Snappy Proof That 123-Avoiding Words are Equinumerous With 132-Avoiding Words

By Doron Zeilberger


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(Exclusively published in the Personal Journal of Shalosh B. Ekhad and Doron Zeilberger)

Written: April 11, 2005.

Many humans fear and dislike recursive algorithms, but computers don't mind them, and I love them. In this particular case, a recursive formulation makes things very transparent and almost trivial. It also makes it very easy to program. In fact here is the very short Maple program .


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