Well the original problem is to show that if f(P) is a scalar field such that f(P_0)=1, and A,B,C are vector fields, then
[\nabla_A,\nabla_B](f(P)C(P))-[\nabla_A,\nabla_B{A}](C(P))=[\nabla_{[A,B]}(C(P))
Unless I am doing something wrong, this immediately reduces to the above identity, which...