Instructions: After you click 'Scramble,' try to restore the numbered arrows to their
correct order and orientation. Hold the mouse button and drag to select a sequence of arrows; when you release
the mouse button, the selected arrows will reverse. You can also select and reverse a single arrow by
clicking on it. 'Undo' undoes. The 'Undo All' button takes you back to the original scrambled configuration. The
'Solve' button, which is active only in the scrambled configuration, steps through an optimal solution
(which may not be unique). This program is a work in progress; please report bugs to email@example.com.