Projective modules over Rees-like algebras and its monoid extensions

Abstract

Let $A$ be a Rees-like algebra of dimension $d$ and $N$ a commutative partially cancellative torsion-free seminormal monoid. We prove the following results. \begin{enumerate} \item Let $P$ be a finitely generated projective $A$-module of $\rank\geq d$. Then $(i)$ $P$ has a unimodular element; $(ii)$ The action of $\EL(A\oplus P)$ on $\Um(A\oplus P)$ is transitive. \item Let $P$ be a finitely generated projective $A[N]$-module of $\rank~r$. Then $(i)$ $P$ has a unimodular element for $r\ge \max \{3,d\}$; $(ii)$ The action of $\EL(A[N]\oplus P)$ on $\Um(A[N]\oplus P)$ is transitive for $r\ge \max \{2,d\}$. \end{enumerate} These improve the classical results of Serre \cite{Se58} and Bass \cite{Ba64}.

There was an error. Proposition 3.5(3) is incomplete and Lemma 3.7 is incorrect. Proposition 3.5(3) and Lemma 3.7 have been used in the proof of Proposition 5.1 and 5.3