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[ayongwust_sjtu <>]

I stepped into << operator of Triangulation_3 with the predefined example :
examples/Triangulation_3/simple_triangulation_3.cpp 

Here is the way the points were inserted in the example:
-------------------------------
  std::list<Point> L;
  L.push_front(Point(0,0,0));
  L.push_front(Point(1,0,0));
  L.push_front(Point(0,1,0));

  Triangulation T(L.begin(), L.end());

  Triangulation::size_type n = T.number_of_vertices();

  // insertion from a vector :
  std::vector<Point> V(3);
  V[0] = Point(0,0,1);
  V[1] = Point(1,1,1);
  V[2] = Point(2,2,2);
-------------------------------
When calling << operator, the triangulation object recursively retrieve all
its vertex iterators, and 
copy them into a TV vector(std::vecotor<Vertex_handle> TV(n+1)).

Then, here are my questions:
1), Why an infinite vertex is defined as the first one of the triangulation?
tr.is_infinite(TV[0]);

2), Why the order of points of the triangulation is different with which
they inserted?
The output order of points is:
1 0 0
0 0 0
0 1 0
1 1 1
2 2 2
0 0 1

While the order in which points were inserted:
  L.push_front(Point(0,0,0));
  L.push_front(Point(1,0,0));
  L.push_front(Point(0,1,0));
.....
  V[0] = Point(0,0,1);
  V[1] = Point(1,1,1);
  V[2] = Point(2,2,2);


Best Regards,
Xianyong Liu

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 Regards, 
 Xianyong Liu 
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