| ?- ?- tree_traversal::orders.
Pre-order:   1 2 4 7 5 3 6 8 9
In-order:    7 4 2 5 1 8 6 9 3
Post-order:  7 4 5 2 8 9 6 3 1
Level-order: 1 2 3 4 5 6 7 8 9
yes