I have two multi picklist fields(A,C) and 1 pick list field(B- yes/no). A has 5 values (1,2,3,4,5) and B has 3 values(7,8,9). If user selects value 1 in A and B pick list value is Yes, user should be able to select 7,8 and save. Subsequently i have different combinations when user selects 1,2,3 in A and b is yes and user should be able to select 7. I know multi pick list supports only few functions like contain, isblank. Is it possible to achieve this via validation rule. Please suggest.