http://en.wikipedia.org/wiki/Tree_search
Node: Each element in the tree is called a node.
Root node: The starting node for a tree.
Child node: The node that appears immediately below a given node is called that node's child nodes. A node can have more than one node.
Parent node: The node immediately above a given node is called that node's parent
Leaf node: A node that doesn't have any children. These nodes are represented at the end of a branch
Sibling node: Nodes that are children of the same parents
Path: A node and all of its ancestors all the way to the root. (Lowe)
Edge: A pointer which connects two nodes
Arc: Another word for an edge that connects two nodes to make a path.
height: The height of a tree is the number of nodes on its longest branch (a path from the root to a leaf).
Binary tree: binary tree is a tree with exactly two sub-trees for each node, called the left and right sub-trees. Although binary or b-trees are frequently discussed in this paper, other type of trees such as r-trees can be transversed as well.
entry: (greedy search) when given several options, try to calculate which situation
will be the best by just considering the direct effect of the option and not any further actions.
then take that option
