More generally, ADT definitions often assume that any operation that changes the state of one ADT instance has no effect on the state of any other instance (including other instances of the same ADT) — unless the ADT axioms imply that the two instances are connected (aliased) in that sense. For example, when extending the definition of an abstract variable to include abstract records, the operation that selects a field from a record variable R must yield a variable V that is aliased to that part of R.