Let k be a field. Given two finite-dimensional right comodules N andM over a k–coalgebra C, the k–vector spaces ExtC(N,M) need not to be finite-dimensional. This is due to the fact that the injective right comodules appearing in the minimal injective resolution of M need not to be of finite dimension or even quasi-finite. The obstruction here is that factor comodules of quasi-finite comodules a...

We show that soluble groups G of type Bredon-FP∞ with respect to the family of all virtually cyclic subgroups of G are always virtually cyclic. In such a group centralizers of elements are of type FP∞. We show that this implies the group is polycyclic. Another important ingredient of the proof is that a polycyclic-by-finite group with finitely many conjugacy classes of maximal virtually cyclic ...

Many advantages of the light-front (LF) formulation for bound state problems arise from the manifest boost invariance in the longitudinal direction [1{5]. The price for this advantage is that other symmetries, such as parity or rotational invariance (for rotations around a transverse axis) are no longer manifest [6,7]. From the technical point of view, the loss of manifest parity and full rotat...

A labelled transition system is provided with some additional structure by endowing the con gurations and the labels with a complete metric In this way a so called metric labelled transition system is obtained The additional structure on a metric labelled transition systemmakes it possible to generalize the niteness conditions nitely branching and image nite to compactly branching and image com...