Closed systems.

(a) Completely closed systems:

(b) Nominally closed systems:

It's a closed system.

It's a closed system. A dead end.

linked analysis is not a closed system.

Alarms. Closed-circuit systems.

A closed system, the Earth is not harmed.

A closed system, the earth is not harmed.

[Anders] A closed system lacks the ability to renew itself.