在這篇博士論文中，我們透過計算Ext_A^{4,*}(H^*(RP^\infty),Z/2) 群來決定在 Ext_A^{5,*}(Z/2,Z/2) 中的不可分元素。而林文雄教授在 [6] 這篇文章裡面，已完全決定了由 Ext_A^{5,*}(Z/2,Z/2)中可分解元素所構成Z/2子模的結構。把這兩個結果結合在一起，就能完全決定Ext_A^{5,*}(Z/2,Z/2)群的結構。

Let A denote the mod 2 Steenrod algebra. In this thesis we determine the indecomposable elements in H^{5,*}(A)
=Ext_A^{5,*}(Z/2,Z/2) by making calculations on the Ext groups
Ext_A^{4,*}(\widetilde{H}^*(RP^\infty),Z/2) for the infinite real projective space RP^\infty. This together with the result of W. H. Lin on the decomposable elements in H^{5,*}(A) completely determine the structure of Ext_A^{5,*}(Z/2,Z/2)$.

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