Include the STL standard header <utility> to define several templates of general use throughout the Standard Template Library.
Four template operators — operator!=, operator<=, operator>, and operator>= — define a total ordering on pairs of operands of the same type, given definitions of operator== and operator<.
If an implementation supports namespaces, these template operators are defined in the rel_ops namespace, nested within the std namespace. If you want to make use of these template operators, write the declaration:
using namespace std::rel_ops;which promotes the template operators into the current namespace.