Prove by resolution refutation that the following set of clauses is unsatisfiable:

{{p(a,y), q(x, f(x))}, {p(z,x), q(y,z)}, {p(x,y), q(g(y), x)}, {p(x, f(a)), q(x,y)}}

Annotate each resolvent with the substitution used and the numbers of parent clauses.