The strength of the two-level hierachical system theory is that there exists a
large number of important systems around us that can be seen as being a twolevel
hierarchical system. Examples considered in [3] and [2] are organisation
structures in large companies, distribution networks, oil refineries and power
plants, to name a few. Consequently it is an interesting question why twolevel
hierarchical systems are so frequent. The following observations might
be at least a partial answer to this question: