Decode the following message, which is produced from a Liv-Zempel code
(the ``substring'' method, not the ``dictionary'' method):
a b b a 3 2 b 4 4 c .
Give the points that appear on the trial hull (in the order that they
appear) when the Graham scan is used to find the convex hull of the
points (6,3) (5,6) (8,2) (2,5) (3,9) and (1,6).