Short videos for the tutorial.
4 1 5 7
4 1 5 6
4 2 3 1
4 1 5 2
4 2 1 3
4 2 3 3
4 2 2 4
4 1 4 4
4 1 4 8
4 1 5 1
4 1 5 4
4 1 5 8