be a primitive p th root of unity and recall that
as ideals in Q
.
Define 
to be the sum on the left side of (1.12) for each j, so that
which belongs to the ideal 
, for 
.
Therefore 
,
belongs to 
. However, since
each 
is a rational integer, it must be divisible by 
where
is the smallest multiple of 
, which is 
,
and (1.12) follows immediately.
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