Modelling Sets by Sequences
Let U: P Person e.g. {Paul, Tom, James}
We can represent the set U by means of an appropriate sequence of people ?:seq:Person, where seq person is the seq of all finite sequences of elements drawn from the type Person e.g.
The abstract data type (ADT) consists of the elements of P person and the operations defined on those sets and the concrete data type (CDT) consists of all the elements of seq Person and the operations defined on those sequences.