Any mathematician is well aware of the following counterintuitive fact: often, the more restrictions you give to your mathematical models the more powerful they become. This is akin to what happens in some artistic disciplines; for instance, for traditional painters it was considered “acceptable” to paint only on a restricted set of materials (frescoes, canvas, wooden panels) using a restricted set of mediums (such as oil). If on one hand this greatly limited the kind of things they could do,...