Dr$.$ Codd published a list of $12$ relational database rules in $1985$; which of the following is not a valid rule?

a$.$ The database must support set$-$level inserts, updates, and deletes.

b$.$ Any database view that is theoretically updatable must be updated outside of the database structure.

c$.$ Every value in a table is guaranteed to be accessible through a combination of table name, primary key value, and column name.

d$.$ Nulls must be represented and treated in a systematic way, independent of data type.