void OBStereo::Permutate(OBStereo::Refs &refs, int i, int j)
 {
   if (i < 0 || i >= refs.size())
     return;
   if (j < 0 || j >= refs.size())
     return;
   unsigned long id = refs.at(i);
   refs[i] = refs.at(j);
   refs[j] = id;
 }
 OBStereo::Refs OBStereo::Permutated(const OBStereo::Refs &refs, int i, int j)
 {
   if (i < 0 || i >= refs.size())
     return refs;
   if (j < 0 || j >= refs.size())
     return refs;
   OBStereo::Refs result(refs);
   result[i] = refs.at(j);
   result[j] = refs.at(i);
   return result;
 }