[Boost-users] how to make fusion::pair less-than-comparable?

Related to my previous question: fusion::map is a sequence and instances of it could be directly compared with operator < , thus vectors of instances also sorted if fusion::pair supported relational operators other than == and != (which it doesn't). So, two questions: 1. What is the recommended way of defining operator< for particular pair instances (e.g. for pair) ? 2. An explanation of why doesn't fusion::pair define at least operator< would be welcome. Thanks. (Yes, I know, I can pass an explicit predicate to std::sort.. )