This is an internal header file, included by other library headers. Do not attempt to use it directly. Instead, include <utility>.
Inclusion of this file has been removed from all of the other STL headers for safety reasons, except std_utility.h. For more information, see the thread of about twenty messages starting with http://gcc.gnu.org/ml/libstdc++/2001-01/msg00223.html, or http://gcc.gnu.org/onlinedocs/libstdc++/faq.html#faq.ambiguous_overloads
Short summary: the rel_ops operators should be avoided for the present.
Definition in file stl_relops.h.