16 Language support library [language.support]

namespace std {
  class weak_equality {
    int value;  // exposition only

    // exposition-only constructor
    explicit constexpr weak_equality(eq v) noexcept : value(int(v)) {}  // exposition only

  public:
    // valid values
    static const weak_equality equivalent;
    static const weak_equality nonequivalent;

    // comparisons
    friend constexpr bool operator==(weak_equality v, unspecified) noexcept;
    friend constexpr bool operator!=(weak_equality v, unspecified) noexcept;
    friend constexpr bool operator==(unspecified, weak_equality v) noexcept;
    friend constexpr bool operator!=(unspecified, weak_equality v) noexcept;
    friend constexpr weak_equality operator<=>(weak_equality v, unspecified) noexcept;
    friend constexpr weak_equality operator<=>(unspecified, weak_equality v) noexcept;
  };

  // valid values' definitions
  inline constexpr weak_equality weak_equality::equivalent(eq::equivalent);
  inline constexpr weak_equality weak_equality::nonequivalent(eq::nonequivalent);
}