You can easily do your != et al from < thing by using CRTP inheriting from a 'comparable' template class that provides the implementations. Sort of thing that should be in std really.
It looks like this isn't attached to the class definition, but rather to the uses. I.e. for every use of a class that only defines ==, <, you have to include rel_ops. But then it would basically provide the other comparators to all classes, maybe not something you'd want.
