I have three columns A B C (hierarchy in a company with C at the highest)

All of them contain names and should have a unique mapping in A, B and C. Person in A works under a person in B who in turn works for the person in C.
How do I ensure, I dont have a name in A mapped with multiple names in B or C? (since the hierarchy for a person in A is fixed i.e. he/she cannot work under multiple persons)