is a revised upgrade of the first edition (1999), with additional recent results on the group of a random walk. The theoretical approach given therein has been developed by the authors since the early 1970s. By using , , , and , completely new methods are proposed for solving functional equations of two complex variables, which can also be applied to characterize the of the walks, as well as to find explicit solutions to the one-dimensional , or to tackle a new class of . weiterlesen