mp_units::operator‐

template<
    std::derived_from<quantity_point> QP,
    QuantityPointOf<absolute_point_origin> QP2>
[[nodiscard]]
constexpr
Quantity auto
operator‐(
    QP const& lhs,
    QP2 const& rhs)
requires requires { lhs.quantity_ref_from(point_origin) ‐ rhs.quantity_ref_from(QP2::point_origin); };