Non-member lexicographical comparisons

template <typename Key, typename T, typename Compare, typename Allocator>
bool operator<( const concurrent_map<Key, T, Compare, Allocator>& lhs,
                const concurrent_map<Key, T, Compare, Allocator>& rhs )

Returns: true if lhs is lexicographically less than rhs.

---

template <typename Key, typename T, typename Compare, typename Allocator>
bool operator<=( const concurrent_map<Key, T, Compare, Allocator>& lhs,
                const concurrent_map<Key, T, Compare, Allocator>& rhs )

Returns: true if lhs is lexicographically less or equal than rhs.

---

template <typename Key, typename T, typename Compare, typename Allocator>
bool operator>( const concurrent_map<Key, T, Compare, Allocator>& lhs,
                const concurrent_map<Key, T, Compare, Allocator>& rhs )

Returns: true if lhs is lexicographically greater than rhs.

---

template <typename Key, typename T, typename Compare, typename Allocator>
bool operator>=( const concurrent_map<Key, T, Compare, Allocator>& lhs,
                const concurrent_map<Key, T, Compare, Allocator>& rhs )

Returns: true if lhs is lexicographically greater or equal than rhs.