"These systems don't retain their military effectiveness forever," he said.

The system still retains many of the elements put in place in 1947.

This means that if a single node breaks down, the system still retains the much of the ability to reconstruct its information.

In spite of all its anomalies, it is difficult to see what other system could have retained even the present small population.

The system didn't actually retain much more water than Earth did; that isn't the problem.

In most areas though, the 1974 system was far more conservative and retained more traditional boundaries.

A system with the property of interoperability will retain that property well into the future.

The current system retains non-democratic elements to the election of the local government.

Despite this pressure for reform, the existing system retains its supporters.

Most such systems retain a small on-board battery to reach the next stop after a power-failure.