Contexting in Crystal Reports

Hi ,

i have a requirement assuming the below data

SO Num    Status  Flag

-----------    ----------  --------

1              A           Yes

1              B           Yes

2              B            No

2              C            No

3              C            Yes

3              C            Yes

3              A            Yes

my flag would be Yes if any of the statuses for a particular SO Num is having A. how to achieve this using a formula in crystal ??

i have to compare all the statuses of a particular SO num. and then update the flag for every row....