Postelection Edit rule - need help with Fast Formula

 Anyone have an example Postelection Edit rule they can share?  There's only one in the Fast Formula reference guide and it's not meeting my needs, or not written correctly, no matter what I try I cannot get the rule to verify.  Can I write a Fast Formula that doesn't have to call a separate function?  All I am looking for is the ability to compare a pl_id for one plan type to an oipl_id elected in another plan type and return ERROR_MESSAGE if oipl_id is not in the ones identified.  The below function will compile, but I cannot seem to