template <class ForwIter, class Predicate>
ForwIter std::remove_if(ForwIter beg, ForwIter end,
                        Predicate op)
{
    while (beg != end && !op(*beg)( {
        ++beg;
    }
    if (beg == end) {
        return beg;
    }
    else {
        ForwIter next = beg;
        return remove_copy_if(++next, end, beg, op);
    }
}