Trees are yet another type of graph. Trees have all the properties of graphs except they must be connected with no cycles. A computer's hard drive directory structure is set up as a tree, with subdirectories branching out from a single root directory. Typically trees have a vertex labeled as the root vertex from which every other vertex can be reached from a unique path along the edges. Not all vertices can be a root vertex. Trees come into importance for devising searching algorithms.
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Science EncyclopediaScience & Philosophy: Cluster compound to ConcupiscenceCombinatorics - History Of Combinatorics, Enumeration, Binomial Coefficients, Equivalence Relations, Recurrence Relations, Graph Theory