Duals of formal group Hopf orders in cyclic groups

Abstract

Let $p$ be a prime number, $K$ be a finite extension of the $p$-adic rational numbers containing a primitive $p^n$th root of unity, $R$ be the valuation ring of $K$ and $G$ be the cyclic group of order $p^n$. We define triangular Hopf orders over $R$ in $KG$, and show that there exist triangular Hopf orders with $n(n+1)/2$ parameters by showing that the linear duals of "sufficiently $p$-adic" formal group Hopf orders are triangular.