Let \(a\) be the vector of bird ages, and \(n\) the vector of sequence lengths so that \(\check{a}=n+1-a\) is reverse age. Show that \(\operatorname{span}\{\mathbf{1}, a /(n+1)\}\) is equal to \(\operatorname{span}\{\mathbf{1}, \check{a} /(n+\) 1)\}. Hence justify the claim made about age reversal in the third of the list of options in Sect. 10.2.