“…In this section, we are going to give a brief introduction to linearization techniques. What became known in the free probability community as the "linearization trick" [51,22,21,3,4,9,39] turned out some years ago to be used extensively also in other branches of mathematics, ranging from system engineering over automata theory to the theory of non-commutative rings ; see [24,32] and the references collected therein. In fact, linearization works equally well for noncommutative rational functions, but we will restrict here to the case of noncommutative polynomials.…”