åpenlukket

Åpenlukket is a Norwegian compound adjective formed from åpen (open) and lukket (closed). It is used to describe entities, systems, or concepts that exhibit both openness and closure, or that are designed to allow extension while maintaining fixed boundaries. The term appears most often in compound phrases rather than as a standalone concept.

In software engineering, the closely related term åpen-lukket prinsippet (the Open-Closed Principle) states that software modules should be open for extension but closed for modification. Proposed by Bertrand Meyer, it guides the design of interfaces and abstractions to accommodate new behavior without changing existing code, thereby reducing regression risk and improving maintainability.

In topology, some sets are both open and closed; in English this is called “clopen.” Norwegian usage may render this as “åpen og lukket samtidig” or, in borrowed form, “klopen.” In the real line with the usual topology, the only clopen sets are the empty set and the entire space; in discrete or other specialized topologies, more sets may be clopen. The concept illustrates that openness and closure are not always mutually exclusive.

Overall, åpenlukket appears primarily in technical contexts to describe systems or concepts that blend openness with a stable, closed boundary. See also open-closed principle, topology, and clopen sets.