Fraser fir tree species. Growing and harvesting this species for Christmas trees and boughs is a multimillion-dollar business in the southern Appalachians. North Carolina produces the majority of Fraser fir Christmas trees. It requires from 7 to 10 years in the field to produce a high tree. In 2005, the North Carolina General Assembly passed legislation making the Fraser fir the official Christmas tree of North Carolina. Fraser fir The Fraser fir ("Abies fraseri") is a species of fir native to the Appalachian Mountains of the Southeastern United States. "Abies fraseri" is closely related to balsam fir ("Abies balsamea"), of which it
Tree walking automaton Tree walking automaton A tree walking automaton (TWA) is a type of finite automaton that deals with tree structures rather than strings. The concept was originally proposed by Aho and Ullman. The following article deals with tree walking automata. For a different notion of tree automaton, closely related to regular tree languages, see branching automaton. All trees are assumed to be binary, with labels from a fixed alphabet Σ. Informally, a tree walking automaton "A" (TWA) is a finite state device which walks over the tree in a sequential manner. At each moment "A" visits a node "v" in state