"The universe is hierarchically organized in a sequence of levels in such a way that the entities on any given level are composed of a finite number of subentities from the next lower level which are united and organized by characteristic interactions. Thus organisms are comprised of cells, cells of molecules, ... It is important to note that on each level of the hierarchy the reality of an entity includes not only the reality of the subentities which compose it but also that of the interactions between them.

Let us use the term 'system' to denote a set of entities united in a coherent pattern of interaction with one another. We can say then that the universe is hierarchically organized in a sequence of systems, in which the systems of each level are composed of subsystems from the next lower level."

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