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*Definition:*
A *tree* is a directed graph such that there is exactly one node,
the *root*, that has indegree zero, every other node
has indegree one, and every node can be reached from the root.

Tis tree : <=>Tis directed graph /\( existsrinV: indeg(r) = 0 /\forallxinV-{r}:indeg( x) = 1 /\xis reachable fromrinT)whereV=T_{0}.root( T) := (suchrinV: indeg(r) = 0)whereV=T_{0}.

Author: Wolfgang Schreiner

Last Modification: January 26, 2000