It's possible to be locally sane. For example, suppose you define an abstract Number class, and define subclasses for ComplexFloat and IntFraction numbers. You

It's possible to be locally sane. For example, suppose you define an abstract Number class, and define subclasses for ComplexFloat and IntFraction numbers. You could define .equals() methods on each of those that only compare to the same type, and work correctly. You don't always have to deal with weird issues.