# Invariant tensors

It is often stated that the Kronecker delta and the Levi-Civita epsilon are the only (irreducible) invariant tensors under the Lorentz transformation. While it is fairly easy to prove that the two tensors are indeed invariant wrt Lorentz transformation, I have not seen a proof that there aren't any more such tensors.

So, my question is, how to find all invariant tensors under some (linear) transformation? Is there a general procedure for this?

Thanks