2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/67280Let $X$ be a normal arithmetically Gorenstein scheme in ${\mathbb P}^n$. We give a criterion for all codimension two ACM subschemes of $X$ to be in the same Gorenstein biliaison class on $X$, in terms of the category of ACM sheaves on $X$. These are sheaves that correspond to the graded maximal Cohen--Macaulay modules on the homogeneous coordinate ring of $X$. Using known results on MCM modules, we are able to determine the Gorenstein biliaison classes of codimension two subschemes of certain varieties, including the nonsingular quadric surface in ${\mathbb P}^3$, and the cone over it in ${\mathbb P}^4$. As an application we obtain a new proof of some theorems of Lesperance about curves in ${\mathbb P}^4$, and answer some questions be raised.Key words and phrases: linkage, liaison, biliaison, Gorenstein scheme, maximal Cohen-Macaulay modules; 30 pagesAlgebraic GeometryCommutative Algebra14M06; 13C40; 13C14text