In solid state physics, the difference between conductors and insulators is modelled and explained. In conductors, electrons can move freely through the solid. In an insulator, on the other hand, the electrons are forced to stay close to respective atoms of the solid. This phenomenon can be understood in the realm of quantum mechanics by the so-called band model. Insulators are characterised by completely occupied bands and an energy gap to the first unoccupied band. As recently discovered, such a filled band can, moreover, have topological invariants. Such “topological insulators” are the subject of the survey article by Hermann Schulz-Baldes. These novel topological properties are responsible for the existence of supplementary conducting modes on boundaries of the system: A topological insulator becomes an excellent conductor on its surface. Certainly, a clothesline will move downwards if one hangs something on it. Similarly one may wonder whether a thin clamped elastic plate will move downwards when being pushed downwards. In terms of the modelling differential equation and boundary conditions the question would be whether a positive source will yield a positive solution. As Guido Sweers outlines in his survey “On sign preservation for clotheslines, curtain rods, elastic membranes and thin plates” the answer is in some cases, as expected, positive. But there are also, at a first glance counterintuitive, models where such a sign preservation property may fail. Sometimes, sign preservation and its failure may be observed even in the same model, depending e.g. on the equilibrium shape of the object being modelled. Norbert Schappacher reviews the book “Emil Artin and Beyond–Class Field Theory and L-Functions” by Della Dumbaugh and Joachim Schwermer, which highlights