+extern void set_points_list(XPoint *points, int npoints, linked_point *root);
+extern void traverse_points_list(linked_point * root);
+extern void draw_three_vertices(linked_point * a, Bool triangle);
+extern double compute_edge_length(linked_point * a, linked_point * b);
+extern double get_angle(double a, double b, double c);
+extern Bool is_same_slope(linked_point * a);
+extern Bool is_an_ear(linked_point * a);
+extern Bool is_three_point_loop(linked_point * head);
+