Some odd permutations

摘要

I recently stumbled on an identity (Theorem 2) that related two types ofpermutations. It looked like one of those serendipitous pieces ofmathematics that led to a simple enumerative resu mostly when thishappens it leads—joyously—to an enumerative proof that was 'blindingly'obvious. Except in this case, it wasn't, I don't think.