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If you can get from a parent to a child using a reference, then you can get back to the parent using the same reference (i.e. there us an "undirected edge" between a parent and child so you can go from parent to child). Leaves have no children and the root cannot be a leaf. The height of a node is the length of the path from that node to the root. OK-ary trees (discussed in class) can be implemented using the "first child, next sibling" method (discussed in the book). A pre-order traversal visits children after processing the node itself. A post-order traversal visits children after processing the node itself. A binary tree has at most 1 child per node (it is binary: 0 or 1 children). Recursion can be used to determine the number of nodes in a tree. Recursion cannot be used to determine the height of a tree (iteration must be used). The textbook provides implementations for pre-, post-, and in order tree iterators