![\begin{picture}(714,193)(20,646)
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\put(480,...
...{\makebox(0,0)[lb]{\raisebox{0pt}[0pt][0pt]{\twlrm next sibling}}}
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Implementation 1: each node needs an array of pointers.
Implementation 2: each node only needs two pointers.
Applications: hierarchies, directories
Depth of a node: length of path from root to node.
Root is at depth 0.
Height of a node: length of longest path from node to leaf.
All leaves have height 0.
The height of the root is the height of the tree.