  Let R be a commutative noetherian ring. Denote by mod R the category of
finitely generated R-modules. In this paper, we study n-torsionfree modules in
the sense of Auslander and Bridger, by comparing them with n-syzygy modules,
and modules satisfying Serre's condition (S_n). We mainly investigate
closedness properties of the full subcategories of mod R consisting of those
modules.
