mp_units::operator<=>

[[nodiscard]]
constexpr
auto
operator<=>(
    quantity_character lhs,
    quantity_character rhs) = default;

[[nodiscard]]
consteval
auto
operator<=>(
    basic_fixed_string const& lhs,
    CharT const(& rhs)[N2]);

[[nodiscard]]
constexpr
auto
operator<=>(
    basic_fixed_string const& lhs,
    basic_fixed_string<CharT, N2> const& rhs);

[[nodiscard]]
constexpr
auto
operator<=>(
    symbol_text const& lhs,
    symbol_text<N2, M2> const& rhs) noexcept;