How to configure Product Rule to select multiselect LOVs

Hi Experts,

There is a EFF configured as multiselect LOV having values A,B,C,D on an Engineering Change Order in PD module

. As per the business logic, user can select - values A orB,C,D.

It means he cannot select A, if he has already selected B or C or D or any of multiselect for B,C,D

Similarly if he selects A, then cannot select B,C,D.

Currently have configured a validation rule -

IF condition - TRUE

Validation Condition -

ChangeHeader,AttributeGroup.EFFName in (ChangeHeader,AttributeGroup.EFFName,"A") AND

ChangeHeader,AttributeGroup.EFFName in (ChangeHeader,AttributeGroup.EFFName,"B""C","D")