The class Triangulation_utils_3 defines operations on the indices of vertices and neighbors within a cell.
#include <CGAL/Triangulation_utils_3.h>

 
In dimension 3, index of the neighbor n that is next to the current cell,
when turning positively around an oriented edge whose endpoints are
indexed i and j. According to the usual numbering of
vertices and neighbors in a given cell, it is also the index of the vertex
opposite to this neighbor n. (see Figure 28.9).
 


Has a meaning only in dimension 2. Computes the index of the vertex that is next to the vertex numbered i in counterclockwise direction. (see Figure 28.9).
 

 Same for clockwise. 
Figure 28.9: Operations on indices.