template<typename iterator> void set_priority(iterator begin, iterator end, list<node*> & output ) {
    list<node*>::iterator i = begin;
    int counter = 0 ;
    while(i != end) {
        if ( *i->parenthesis == '(' ) counter += 10 ;
        else
            if ( *i->parenthesis == ')' ) counter -= 10 ; 
        else
            if (i->operation) (*i)->operation->priority += counter ;
    }
}