John Fraser (botanist) of botany and natural science." Species named after Fraser include, among others, "Abies fraseri" (Fraser Fir), "Magnolia fraseri" (Fraser Magnolia), and the gentianworts, "Frasera". A 50-foot Fraser Fir was used in 1998 as the U.S. Capitol Christmas Tree; the species was also used in 1974. The Fraser's Saint John's wort ("Triadenum fraseri") is named in honour of Fraser. John Fraser's letters are maintained at the Royal Society of Arts, and one of his portraits hung at the Hunt Library. Both Hoppner and Raeburn painted his portrait. Fraser was an elected fellow of both the Linnean Society of London (FLS 1810)
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