Coflat Modules and Exact Sequence

Abstract

We know that a right R-module C is flat if and only if every short exact sequence O→A→B→C→O of right R-modules is pure. Dually a right R-module A is coflat if ever short exact sequence O→A→B→C→O of right R-modules is copure. Co flat modules are defined in several ways, (as shown in [2] and [4]), In this paper it has shown that these definitions are equivalents. And we shell prove that every direct sum of coflat modules is coflat.