I have three problems that I'm really stuck on. Perhaps someone could give me a pointer on how to start, I literally have no idea, but perhaps a step or two would help.

1) Prove that an arc-length parametrised curve y(s) is planar iff it has an adapted frame such that \kappa_n = \tau = 0.

2) Prove that any two parallel frames of a curve y(t) are related by a constant rotation in the normal plane.

3) Express curvature and torsion of a Frenet curve in terms of \kappa_n and \kappa_g of a parallel frame, and vice versa.

Thanks!