I am going through the Vatti Arbitrary Polygon Clipping Algorithm, but got stuck at their very initial explanation. It says the following:Call an edge of a polygon a left or right edge if the interior of the polygon is to the right or left, respectively. Horizontal edges are considered to be both left and right edges. A key fact that is used by the Vatti algorithm is that polygons can be represented via a set of left and right bounds which are connected lists of left and right edges, respectively, that come in pairs. Each of these bounds starts at a local minimum of the polygon and ends at a local maximum. Consider the polygon with vertices $\{p_0, p_1, ..., p_8\}$ shown in Figure 1(a). The two left bounds have vertices $\{p_0, p_8, p_7, p_6\}$ and $\{p_4, p_3, p_2\}$, respectively. The two right bounds have vertices $\{p_0, p_1, p_2\}$ and $\{p_4, p_5, p_6\}$.The image it refers to is:I do not understand the vertices of the second left bound $\{p_4,p_3,p_2\}$. How are these vertices derived? 
Explanation of the Vatti clipping algorithm
algorithm;polygon