Higher-order correction and normalization

In the brief original paper of VS [195], the hint that the authors used higher-order expansions of the tension $f(k)$ as a function of $k$ is given. Here I present what I have found to be the most practical implementation of such corrections. Some of this has been developed through conversations with Vergini. `Automatic' normalization was already presented in Vergini's thesis [194]; the only new result I have added is the observation of the power-law norm error growth.