The class tt(std::weak_equality)hi(weak_equality) is used when implementing
the spaceship operator for classes that only support (in)equality comparisons,
but not substitutability. The class provides free functions 
tt(operator==) and tt(operator!=) expecting tt(weak_equality) arguments (one
argument may be 0) and it defines two static objects:
    itemization(
    itt(weak_equality::equivalent), indicating equality;
    itt(weak_equality::nonequivalent), indicating non-equality;
    )

Note: at the current release of the Gnu bf(C++) compiler (10.0.0) this class
is not yet available in the tthi(compare) header file.


