/usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.4/include/g++-v3/bits/stl_iterator.h: In 
   constructor `__gnu_cxx::__normal_iterator<_Iterator, 
   _Container>::__normal_iterator(const __gnu_cxx::__normal_iterator<_Iter, 
   _Container>&) [with _Iter = const std::pair<node*, double>*, _Iterator = 
   std::pair<node*, double>*, _Container = std::vector<std::pair<node*, 
   double>, std::allocator<std::pair<node*, double> > >]':
sma.cpp:250:   instantiated from here
/usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.4/include/g++-v3/bits/stl_iterator.h:598: error: invalid
   conversion from `const std::pair<node*, double>* const' to `std::pair<node*, 
   double>*'