Theorem 9.8 of Atiyah : why does it suffice to show for integral ideal in Ap?

93 Views Asked by At

I'm trying to prove => part of atiyah 9.8. I understood everything but enter image description here

Can somebody help me to understand why does it suffice to show for integral ideal of Ap?

1

There are 1 best solutions below

0
On BEST ANSWER

I know why it suffices to show integral ideal (instead of fractional ideal).

Suppose every integral ideal is invertible - (1).

Let M be a nonzero fractional ideal of A. Then there is nonzero x in A s.t. xM is in A. Now since xM is integral ideal, there is a A-submodule N of Frac(A) s.t. (xM)N=A by (1). Note that xN is a A-submodule N of Frac(A) and M(xN)=(xM)N=A.

So we can show that every fractional ideal is invertible.