English

On Group bijections $\phi $ with $\phi(B)=A$ and $\forall a\in B, a\phi(a) \notin A$

Combinatorics 2008-12-16 v1

Abstract

A {\em Wakeford pairing} from SS onto TT is a bijection ϕ:ST\phi : S \to T such that xϕ(x)T,x\phi(x)\notin T, for every xS.x\in S. The number of such pairings will be denoted by μ(S,T)\mu(S,T). Let AA and B B be finite subsets of a group GG with 1B1\notin B and A=B.|A|=|B|. Also assume that the order of every element of BB is B\ge |B|. Extending results due to Losonczy and Eliahou-Lecouvey, we show that μ(B,A)0.\mu(B,A)\neq 0. Moreover we show that μ(B,A)min{B+13,B(qB1)2qB4},\mu(B,A)\ge \min \{\frac{||B|+1}{3},\frac{|B|(q-|B|-1)}{2q-|B|-4}\}, unless there is aAa\in A such that Aa1B=B1|Aa^{-1}\cap B|=|B|-1 or Aa1Aa^{-1} is a progression. In particular, either μ(B,B)min{B+13,B(qB1)2qB4},\mu(B,B) \ge \min \{\frac{||B|+1}{3},\frac{|B|(q-|B|-1)}{2q-|B|-4}\}, or for some aB,a\in B, Ba1Ba^{-1} is a progression.

Cite

@article{arxiv.0812.2522,
  title  = {On Group bijections $\phi $ with $\phi(B)=A$ and $\forall a\in B, a\phi(a) \notin A$},
  author = {Yahya Ould Hamidoune},
  journal= {arXiv preprint arXiv:0812.2522},
  year   = {2008}
}
R2 v1 2026-06-21T11:51:39.164Z