//begin constructor _const_boundary_iterator( Complex& _complex, Cell_boundary & _bd, const typename Complex::Cell& cell): complex( &_complex), next_term ( _bd.begin( cell)), end_term( _bd.end( cell)){ _next_term(); }
//begin constructor _const_filtration_boundary_iterator( Filtration& _f, Cell_boundary & _bd, const Iterator& cell): filtration( &_f), complex( &(_f.complex())), //begin ( _f.begin()), next_term ( _bd.begin( (*cell)->first)), //future_term( next_term), end_term( _bd.end( (*cell)->first)){ _next_term(); }