The line A n ⋆ = A n / 4 T {\displaystyle {\mathcal {A}}_{n}^{\star }={\mathcal {A}}_{n}/{4T}} is a misprint and should in fact be A n = D n / 4 T {\displaystyle {\mathcal {A}}_{n}={\mathcal {D}}_{n}/{4T}} .