The basic idea of Graham's algorithm is simple. Assume that we are given
a point 
inside the hull, and further assume that no three
points in the given set (including 
) are collinear. Sort the
points by angle, counter clockwise about 
. The points are now
processed in their sorted order, and the hull grown incrementally around
the set. At any step, the hull will be correct for the points examined so
far. The hull so far is maintained in a stack 
of points. Initially,
the stack contains the first two points in the sorted list,
. The next point 
is added, if the
set of three points 
make a left turn at
. This implies that 
is a
convex chain, a condition that will be maintained throughout for all the
points in the stack.