Diametral dimensions of Frechet spaces

The diametral dimension is an important topological invariant in the category of Frechet spaces which has been used, e.g., to distinguish types of Stein manifolds. We introduce variants of the classical definition in order to solve an old conjecture of Bessaga, Mityagin, Pelczynski, and Rolewicz at least for nuclear Frechet spaces. Moreover, we clarify the relation between an invariant recently introduced by Terzioglu and the by now classical condition $(\bar \Omega)$ of Vogt and Wagner.