There are many dangers external to the space shuttle's protective skin. A Whole is perceived by observers for its function on its own, instead for its specific relationships, subsystems, and parts. It quasi hides or has hidden its internal relationships from observation. Boundary collects all of the unobserved relationships in a system being observed, making wholes or entities. The boundary between the U.S. and Mexico is guarded closely.
Entities expose their wholeness to observation.
Any entity, whether individual, corporation, or government, is welcome to apply. Members are entities defining their relationships. In order to be a member of that association, one must be at least 55 years of age. Closed excludes external relationship. His eyes closed, he concentrated on repeating a mantra without visual distraction.