associative_range(S2 &seq)
: m_position(seq.begin())
, m_last(seq.end())
{}
static inline void set_difference(const S1 &src1, const S2 &src2, D &dst) {
std::set_difference(
src1.begin(), src1.end(), src2.begin(), src2.end(),
std::inserter(dst, dst.begin()));
}
