Some characterizations of relative sequentially Cohen–Macaulay and relative Cohen–Macaulay modules
Abstract
Let M be an R-module over a Noetherian ring R and 𝔞 an ideal of R with c=cd(𝔞,R). First, over an 𝔞-relative Cohen–Macaulay local ring (R,𝔪), we provide a characterization of the 𝔞-relative sequentially Cohen–Macaulay modules M in terms of 𝔞-relative Cohen–Macaulayness of the R-modules Extc−iR(M,D𝔞) for all i≥0, where D𝔞=HomR(Hc𝔞(R),E(R/𝔪)). Next, we prove that M is finite 𝔞-relative Cohen–Macaulay if and only if Hi(LΛ𝔞(Hcd(𝔞,M)𝔞(M)))=0 for all i≠cd(𝔞,M) and Hcd(𝔞,M)(LΛ𝔞(Hcd(𝔞,M)𝔞(M)))≅ˆM𝔞. Finally, we provide another characterization of 𝔞-relative sequentially Cohen–Macaulay modules M in terms of vanishing of the local homology modules Hj(LΛ𝔞(Hi𝔞(M)))=0 for all 0≤i≤cd(𝔞,M) and for all j≠i.
Communicated by P. Ara