Introduction

Abstract

The reader may find the concept of a “tree” used in this book a very generous one. On reflection we see that a tree is not easily defined or at least is definable in many different ways. Trees, in fact, are no longer the property of botanists, since to a mathematician a “tree” is a system in which any two points are connected via only one possible pathway (i.e., the system is not a reticulum and lacks loops). In this very general sense one may find trees in many disciplines — in heraldry as a genealogical chart (a family tree), in geomorphology as the tributaries of a stream system, in cybernetics as a decision-making process, each providing an example of a mathematical tree. The dichotomous key on page 84 is an example of such a tree.