move closure property to discussion references

doc/manual/src/architecture/store/objects.md

@@ -35,21 +35,6 @@ A bare file or symlink can be a root file system object.
 
 Symlinks pointing outside of their own root, or to a store object without a matching reference, are allowed, but might not function as intended.
 
-## Reference {#reference}
-
-A store object can reference other store objects.
-
-Nix stores have the *closure property*: for each store object in the store, all the store objects it references must also be in the store.
-
-Building, copying and deleting store objects must be done in a way that obeys this property:
-
-- Build results must only refer to store objects in the closure of the build inputs.
-
-- Store objects being copied must refer to objects already in the destination store.
-  Recursive copying must either proceed in dependency order or be atomic.
-
-- We can only safely delete unreferenced objects.
-
 ### Reference scanning
 
 While references could be arbitrary paths, Nix requires them to be store paths to ensure correctness.

doc/manual/src/architecture/store/store.md

@@ -52,12 +52,23 @@ References are [opaque][opaque-data-type], [unique identifiers][unique-identifie
 The only way to obtain references is by adding or building store objects.
 A reference will always point to exactly one store object.
 
-An added store object cannot have references, unless it is a build task.
+Nix stores have the *closure property*: for each store object in the store, all the store objects it references must also be in the store.
+
+Adding, building, copying and deleting store objects must be done in a way that obeys this property:
+
+- A newly added store object cannot have references, unless it is a build task.
+
+- Build results must only refer to store objects in the closure of the build inputs.
 
   Building a store object will add appropriate references, according to provided build instructions.
-These references can only come from declared build inputs, and are not known to build instructions a priori.
+  These references can only come from declared build inputs.
+
+- Store objects being copied must refer to objects already in the destination store.
+
+  Recursive copying must either proceed in dependency order or be atomic.
+
+- We can only safely delete store objects which are not reachable from any reference still in use.
 
-A store object cannot be deleted as long as it is reachable from a reference still in use.
   Garbage collection will delete all store objects that cannot be reached from any reference in use.
 
   <!-- more details in section on garbage collection, link to it once it exists -->