Validation in FI

Hi friends,

I am using validation in accounting (tcode OB28) to set rules for internal order and GL account. There are 167 internal order to be assigned to one GL account. However the Boolean rules only allowed several internal order numbered being entered in prerequisites. Thus it can't be saved. Therefore, how am i going to emphasized correct internal order numbers to be used by the user in the system. Appreciate your feedback.

Thanks