# Talk:Alternating permutation

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Field:  Algebra

## Zigzag & alternating meaning

There seems to be some variation in the sources as to the definitions. For example Mathworld does not require c1< c2 for alternating permutation but Sloane does. I've tried to create the most reasonable compromise in which An is the number of alternating permutations and Zn is the number of zigzag permutations, where An and Zn are as used in Mathworld.--RDBury (talk) 15:06, 18 January 2009 (UTC)

## Notation / Minor errors

Why is the number of alternating permutations denoted by A_n in Section 1 and by E_n in section 2? Also in the proof of André's Thm, "The number of ways to choose a permutation of {1,...,n+1} that is either alternating or reverse-alternating is E_(n+1)" should be 2 E_(n+1), right? In the second step of the combinatorial proof of the identity, "choose a reverse-alternating permutation ... of the set {1,...,k}" should rather refer to the subset of size k chosen in the first step (this is not necessarily {1,...k}). Similarly, the set in the third step should be the complement of the chosen subset. Right? -- Martin B. --85.181.225.53 (talk) 09:42, 11 July 2015 (UTC)

## Assessment comment

The comment(s) below were originally left at Talk:Alternating permutation/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

 Geometry guy 00:32, 22 May 2007 (UTC) What 'c1< c2' means? —Preceding unsigned comment added by 130.231.62.1 (talk) 12:58, 7 May 2008 (UTC)

Last edited at 12:59, 7 May 2008 (UTC). Substituted at 01:45, 5 May 2016 (UTC)