DEBUG: 6

DEBUG: b

DEBUG: a

DEBUG: 5

DEBUG: 4

DEBUG: 3

DEBUG: more to undo? true

DEBUG: -3

DEBUG: -4

DEBUG: -5

DEBUG: -a

DEBUG: -b

DEBUG: -6

DEBUG: more to undo? true

DEBUG: 6

DEBUG: b

DEBUG: a

DEBUG: 5

DEBUG: 4

DEBUG: 3

DEBUG: more to undo? true

DEBUG: -3

DEBUG: -4

DEBUG: -5

DEBUG: -a

DEBUG: -b

DEBUG: -6

DEBUG: more to undo? true

DEBUG: 6

DEBUG: b

DEBUG: a

DEBUG: 5

DEBUG: 4

DEBUG: 3

DEBUG: more to undo? true

DEBUG: 2

DEBUG: more to undo? true

DEBUG: -2

DEBUG: more to undo? true

DEBUG: 2

DEBUG: 1

DEBUG: more to undo? false

DEBUG: -1

DEBUG: 1

DEBUG: more to undo? false