- If a tree is null, then the empty list is the preorder, inorder, and
postorder listing of
*T* - If
*T*comprises a single node, that node itself is the preorder, inorder, and postorder list of*T* - Otherwise
- 1.
- The preorder listing of
*T*is the root of*T*, followed by the nodes of*T*_{1}in preorder, . . . , and the nodes of*T*_{k}in preorder. - 2.
- The inorder listing of
*T*is the nodes of*T*_{1}in inorder, followed by the root*r*, followed by the nodes of*T*_{2}in inorder, . . . , and the nodes of*T*_{k}in inorder. - 3.
- The postorder listing of
*T*is the nodes of*T*_{1}in postorder, . . . , the nodes of*T*_{k}in postorder, all followed by the root*r*.

**Example**: see Figure 4.2.- Preorder 1,2,3,5,8,9,6,10,4,7
- Postorder 2,8,9,5,10,6,3,7,4,1
- Inorder 2,1,8,5,9,3,10,6,7,4

- Note that the order of appearance of the leaves is the same in all the three schemes. This is true in general.