Top 10 customer available in last month but not in Current month

[#1]

Hi All, Can Anyone help me to get Top 10 customer from last month those are out from the list of top 10 customer of Current month. Let say i am having Top 10 customer for Jan-2011, And Top 10 customer for Feb-2011 Now i want those customer only those are present in jan top10 list but not in Feb top 10 list. I am having expression for year like "TOP 10 CUSTOMER IN PREVIOUS YEAR BUT NOT PRESENT IN CURRENT YEAR"

EXPRESSION FOR YEAR SCENARIO:

=IF(
aggr(
rank(total
aggr( Sum( {<Year={"$(=year(Max(TRANSACTION_DATE))-1)"}>}
SalesDetail_Amt),CUSTOMER_ID)
,0,1)
,CUSTOMER_ID)
<='$(VTop)',
IF(
aggr(
rank(total
aggr(Sum( {<Year={"$(=year(Max(TRANSACTION_DATE)))"}>}
SalesDetail_Amt),CUSTOMER_ID)
,0,1)
,CUSTOMER_ID)
>'$(VTop)'
OR
ISnull(aggr(
rank(total
aggr(Sum( {<Year={"$(=year(Max(TRANSACTION_DATE)))"}>}
SalesDetail_Amt),CUSTOMER_ID)
,0,1)
,CUSTOMER_ID))
=-1,
CUSTOMER_ID))