Let R be the relation on the set of people with doctorates such that (a, b)

Question:

Let R be the relation on the set of people with doctorates such that (a, b) ∈ R if and only if a was the thesis advisor of b. When is an ordered pair (a, b) in R2? When is an ordered pair (a, b) in Rn, when n is a positive integer? (Assume that every person with a doctorate has a thesis advisor.)