Arrange for the areas between contour lines drawn to be C shaded. C C Compute and print statistics for the plot and label it. If any area identifier is negative, turn off drawing. If drawing is turned on, draw the polyline. C C Done.
C C Turn off shading.
If the area identifier for group 3 is in the right range, turn on C shading. If shading is turned on, shade the area. The last point of the C edge is redundant and may be omitted. C C Done.