Summary

• Child entities which are both mutable and shared can make any, or all of their parents invalid.
• In freeform shared mutability, we cannot cache any calculation that depends on a shared mutable entity.
• If we limit the scope of sharing to code we trust not to invalidate our cache, then we can cache results as much as we like.
• Limiting the scope of sharing implies that we have some kind of container entity: an Arena.