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			bool erase_immediately;

			std::vector<VertexIter> unused_vertices;

			std::vector<FaceIter> unused_faces;

			std::vector<HalfEdgeIter> unused_halfedges;

			Manifold(const Manifold&) {}

			const Manifold& operator=(const Manifold&) {return *this;}

			Manifold(): erase_immediately(true) {}

			///< Construct an empty manifold.

			bool is_valid();

			/**< Performs a series of tests to check that this is a valid manifold.

				 This function is not rigorously constructed but seems to catch

				 all problems so far. The function returns true if the mesh is 

				 valid and false otherwise.	*/

			void enumerate_vertices();

			/**< Give each vertex a unique id corresponding to its iterator

				 position */

			void enumerate_halfedges();

			/**< Give each halfedge a unique id corresponding to its iterator

				 position */

			void enumerate_faces();

			/**< Give each face a unique id corresponding to its iterator

				 position */

			size_t no_faces() const {return face_db.size();}

			///< Return the number of faces.

			size_t no_halfedges() const {return halfedge_db.size();}

			///< Return the number of halfedges.

			size_t no_vertices() const {return vertex_db.size();}

			///< Return the number of vertices

			VertexIter create_vertex(const CGLA::Vec3f& pos);

			///< Create a new vertex.

			FaceIter create_face();

			/**< Create a new face.

				 An iterator to the face is returned. When a face f is initially

				 created, is_used(f) will return false. */

			HalfEdgeIter create_halfedge();

			/**< Create a new halfedge. An iterator to the halfedge is returned.

				 When h is initially created, is_used(h) returns false. */

			void clear();

			///< Clear the manifold, removing all data.

			void remove_unused();

			/**< Remove unused vertices, edges and faces from the database.

				 If delayed_erase mode is enabled, then until this function 

				 has been called, erased vertices, edges, and faces are just marked

				 as unused but not removed from their respective lists. */

			void delayed_erase();

			/**< Delay the actual removal of vertices, faces, and edges that

				 are erased.  In many cases, it is a problem if one cannot

				 test whether a vertex, halfedge, or face indicated by an

				 iterator is in use or has been removed from the mesh. One

				 solution to this problem is to delay the actual removal of

				 the vertex, edge or face. Instead when calling, say,

				 erase_face(f), all the iterators of f are assigned the

				 appropriate NULL value to indicate that they are not

				 pointing at anything, and f is added to a vector of faces

				 that need to be physically removed from the face_db.

				 Since f is not erased, all iterators pointing at f remain

				 valid! And, importantly, it is possible to test whether f is

				 in use by calling is_used(f).

				 When remove_unused is called, the physical removal takes

				 place. Calling immediate_erase switches Manifold back to the

				 state where entities are removed as soon as the appropriate

				 erase function is called, and at the same time calls

				 remove_unused.

			*/

			void immediate_erase();

			/**< Immediately remove erased entities.

				 Calling immediate_erase switches Manifold back to the state

				 where entities are removed as soon as the appropriate erase

				 function is called.

				 See delayed_erase for more details, and note that

				 immediate_erase is the default mode.  */

			bool is_used(VertexIter v) const;

			/**< Test whether the vertex indicated by the argument v is used.

				 This function returns true if the vertex appears to have a 

				 valid outgoing halfedge iterator. */

			bool is_used(FaceIter f) const;

			/**< Test whether the face indicated by the argument f is used.

				 This function returns true if the face appears to have a 

				 valid halfedge iterator. */

			bool is_used(HalfEdgeIter h) const;

			/**< Test whether the halfedge indicated by the argument h is used.

				 This function returns true if the halfedge appears to have a 

				 valid vertex iterator. */

			void erase_halfedge(HalfEdgeIter h);			

			/**< Erase halfedge h. 

				 In general, you should never call this function but use the 

				 collapse_halfedge function instead since blindly erasing geometry

				 is most likely to invalidate the Mesh. Quite possibly this function

				 will be removed from the public interface. 

				 Note that if delayed_erase has been called, this function does

				 not immediately remove anything from the mesh. Instead the halfedge

				 is reset to its initial state. Thus, iterators are not invalidated,

				 and it is possible to test whether h is used calling:

				 is_used(h). when remove_unused is called, the actual removal

				 takes place.

			*/

			void erase_vertex(VertexIter v);

			/**< Erase vertex v.

				 In general, you should never call this function but use the 

				 collapse_halfedge function to collapse the vertex away.

				 Blindly erasing is extremely likely to invalidate the

				 Mesh. Quite possibly this function will be removed from the

				 public interface. 

				 Note that if delayed_erase has been called, this function does

				 not immediately remove anything from the mesh. Instead the halfedge

				 is reset to its initial state. Thus, iterators are not invalidated,

				 and it is possible to test whether v is used calling:

				 is_used(v). when remove_unused is called, the actual removal

				 takes place.

			*/

			void erase_face(FaceIter f);

			/**< Erase face f.

				 In general, you should never call this function but use 

				 collapse_halfedge in conjunction with other functions to

				 remove the face through (Euler) operations which preserve

				 the mesh in a valid state.

				 Blindly erasing is extremely likely to invalidate the

				 Mesh. Quite possibly this function will be removed from the

				 public interface. 

				 Note that if delayed_erase has been called, this function does

				 not immediately remove anything from the mesh. Instead the face

				 is reset to its initial state. Thus, iterators are not invalidated,

				 and it is possible to test whether f is used calling:

				 is_used(f). when remove_unused is called, the actual removal

				 takes place.

			*/

			HalfEdgeIter halfedges_begin();

			///< Return iterator pointing to the first halfedge.

			HalfEdgeIter halfedges_end();

			///< Return iterator pointing to beyond the last halfedge.

			VertexIter vertices_begin();

			///< Return iterator pointing to the first vertex.

			VertexIter vertices_end();

			///< Return iterator pointing to beyond the last vertex.

			FaceIter faces_begin();

			///< Return iterator pointing to the first face.

			FaceIter faces_end();

			///< Return iterator pointing to beyond the last face.

			bool collapse_precond(HalfEdgeIter h);

			/**< \brief HalfEdge collapse precondition.

			The argument h is the halfedge we want to collapse. 

			If this function does not return true, it is illegal to collapse

			h. The reason is that the collapse would violate the manifold property

			of the mesh.

			The test is as follows.

			1. For the two vertices adjacent to the edge, we generate

			a list of all their neighbouring vertices. We then generate a 

			list of the vertices that occur in both these lists. That is, 

			we find all vertices connected by edges to both endpoints

			of the edge and store these in a list.

			2. For both faces incident on the edge, check whether they

			are triangular. If this is the case, the face will be removed,

			and it is ok that the the third vertex is connected to both 

			endpoints. Thus the third vertex in such a face is removed

			from the list generated in 1.

			3. If the list is now empty, all is well. Otherwise, there

			would be a vertex in the new mesh with two edges connecting

			it to the same vertex. Return false.

			4. TETRAHEDRON TEST:

			If the valency of both vertices is 

			three, and the incident faces are triangles, we also disallow

			the operation. Reason: It introduces a vertex of valency two

			and if the final two polygons incident on the vertices 

			that are adjacent to the edge being collapsed are triangles, then

			the construction will collapse

			5. VALENCY 4 TEST:

			If a face adjacent to the edge being collapsed is a triangle,

			it will disappear, and the valency of the final vertex beloning to

			this edge will be reduced by one. Hence this valency should be at

			least 4. A valency three vertex will be reduced to a valency two

			vertex which is considered illegal.

			6. PREVENT MERGING HOLES:

			We do not want to collapse an edge if its end points are boundary

			vertices, but its two adjacent faces are not NULL faces, because

			in that case we create a vertex where two holes meet. A non manifold

			situation.	*/

			void collapse_halfedge(HalfEdgeIter h, bool=false);

			/**< Collapse the halfedge h.

			The argument h is the halfedge being removed. The vertex 

			v=h->opp->vert is the one being removed while h->vert survives.

			The final argument is a boolean indicating whether the vertex

			that survives the collapse should have a position which is the

			average of its own position and the vertex that is removed.

			By default false meaning that the surviving vertex retains it 

			position.

			This function is not guaranteed to keep the mesh sane unless,

			collapse_precond has returned true !!

			*/

			FaceIter split_face(FaceIter f, VertexIter v0, VertexIter v1);

			/**< Split a face.

				 The face, f, is split by connecting two

				 vertices v0 and v1 (the next two arguments). The vertices of

				 the old face between v0 and v1 (in counter clockwise order) 

				 continue to belong to f. The vertices between v1 and 

				 v0 belong to the new face. An iterator to the new face is 

				 returned. */

			VertexIter split_edge(HalfEdgeIter h);

			/**< Insert a new vertex on halfedge h.

				 The new halfedge is insterted as the previous edge to h.

				 An iterator to the inserted vertex is	returned. */

			void triangulate(FaceIter f);

			/**< Triangulate a polygonal face by repeatedly calling split_face.

				 Triangulate iteratively splits triangles off a polygon. The first 

				 triangle split off is the one connecting f->last->vert and

				 f->last->next->next->vert.

			*/

			VertexIter safe_triangulate(FaceIter f);

			/**< Triangulate a polygon, f, by inserting a vertex at the barycenter.

				 All vertices in f are connected to the new vertex.				

				 The word "safe" means that it is less likely to create flipped

				 triangles than the normal triangulate. On the other hand, it 

				 introduces more vertices and probably makes the triangles more

				 acute. This function simply calls face_insert_point.

				 The inserted vertex is returned.

			*/

			void face_insert_point(FaceIter f, VertexIter v);

			/**< Insert a new vertex, v, in a face, f.

				 This operation splits an N-gon into N triangles.

				 In the current implementation the original face is erased. 

				 This means that the iterator is not valid after the function

				 returns. 

			*/

			bool merge_faces(FaceIter f, HalfEdgeIter h);

			/**< Merges two faces into a single polygon. The first face is f.  The

				 second face is adjacent to f along the halfedge h. This function

				 returns true if the merging was possible and false

				 otherwise. Currently merge only fails if the mesh is already

				 illegal. Thus it should, in fact, never fail. */

			bool flip(HalfEdgeIter h);

			/**< Flip an edge h. Returns false if flipping cannot be performed.

				 This is either because one of the two adjacent faces is not

				 a triangle, or because either end point has valency three or

				 because the vertices that will be connected already are. */

			void get_bbox(CGLA::Vec3f& pmin, CGLA::Vec3f& pmax);

			/**< Return the bounding box of the manifold. The arguments pmin and pmax

				 will contain the extreme corners of the box when the function 

				 returns.	*/

			void get_bsphere(CGLA::Vec3f& c, float& r);

		};

		{

			return halfedge_db.begin();

		}

	inline HalfEdgeIter Manifold::halfedges_end() 

		{

			return halfedge_db.end(); 

		}

		{

		}

		{

		}

		{ 

		}

			erase_immediately = true;

			if(v->he == NULL_HALFEDGE_ITER)

			return true;