How do two atomic formulas unify?

Question

I have learned loves(bob,Y) and loves(X,santa) can unify because {Y\santa,X\bob}. However, I'm not sure if the following can be unified:

m(a,X) and n(Y,b)

Answer 1

In order for unification the functors must match exactly. That is m and n are two different functors hence the entire expression cannot unify. In the first example the functors for both expressions are the same.