diff --git a/Common/xyzv.h b/Common/xyzv.h
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+++ b/Common/xyzv.h
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+#ifndef _XYZV_H_
+#define _XYZV_H_
+
+// Copyright (C) 1997-2006 C. Geuzaine, J.-F. Remacle
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+// USA.
+// 
+// Please report all bugs and problems to <gmsh@geuz.org>.
+
+#include <set>
+
+using namespace std;
+
+struct xyzv
+{
+  double x, y, z, *vals;
+  int nbvals;
+  int nboccurences;
+  static double eps;
+  xyzv(double xx, double yy, double zz)
+    : x(xx), y(yy), z(zz), vals(0), nbvals(0), nboccurences(0)
+  {
+  }
+  ~xyzv()
+  { 
+    if(vals) delete [] vals; 
+  }
+  xyzv(const xyzv & other)
+  {
+    x = other.x;
+    y = other.y;
+    z = other.z;
+    nbvals = other.nbvals;
+    nboccurences = other.nboccurences;
+    if(other.vals && other.nbvals) {
+      vals = new double[other.nbvals];
+      for(int i = 0; i < nbvals; i++)
+	vals[i] = other.vals[i];
+    }
+  }
+  xyzv & operator =(const xyzv &other)
+  {
+    if(this != &other) {
+      x = other.x;
+      y = other.y;
+      z = other.z;
+      nbvals = other.nbvals;
+      nboccurences = other.nboccurences;
+      if(other.vals && other.nbvals) {
+	vals = new double[other.nbvals];
+	for(int i = 0; i < nbvals; i++)
+	  vals[i] = other.vals[i];
+      }
+    }
+    return *this;
+  }
+  void update(int n, double *v)
+  {
+    if(!vals) {
+      vals = new double[n];
+      for(int i = 0; i < n; i++)
+	vals[i] = 0.0;
+      nbvals = n;
+      nboccurences = 0;
+    }
+    else if(nbvals != n) {
+      throw n;
+    }
+    double x1 = (double)(nboccurences) / (double)(nboccurences + 1);
+    double x2 = 1. / (double)(nboccurences + 1);
+    for(int i = 0; i < nbvals; i++)
+      vals[i] = (x1 * vals[i] + x2 * v[i]);
+    nboccurences++;
+  }
+};
+
+struct lessthanxyzv
+{
+  bool operator () (const xyzv & p2, const xyzv & p1)const
+  {
+    if(p1.x - p2.x > xyzv::eps)
+      return true;
+    if(p1.x - p2.x < -xyzv::eps)
+      return false;
+    if(p1.y - p2.y > xyzv::eps)
+      return true;
+    if(p1.y - p2.y < -xyzv::eps)
+      return false;
+    if(p1.z - p2.z > xyzv::eps)
+      return true;
+    return false;
+  }
+};
+
+typedef set < xyzv, lessthanxyzv > xyzv_cont;
+typedef xyzv_cont::const_iterator xyzv_iter;
+
+#endif