and

Let A denote the mod 2 Steenrod algebra. In this paper we make calculations to completely determine the Ext groups Ext A 4 , ∗ ( Z / 2 , Z / 2 ) and also to determine the structure of Z / 2 -submodule of decomposable elements in Ext A 5 , ∗ ( Z / 2 , Z / 2 ) .