An important concept in the expression language (and Lisp) is that of the
external representation of an object as a sequence of characters.
For example,
an external representation of the integer 28 is the sequence of
characters 28, and an external representation of a list consisting
of the integers 8 and 13 is the sequence of characters (8 13).
The external representation of an object is not necessarily unique. The
list in the previous paragraph also has the representations ( 08 13
) and (8 . (13 . ())).
Many objects have external representations, but some, such as
procedures, do not.
An external representation may be written in an expression to obtain the
corresponding object.
External representations may also be used for communicating
between processes defined in this International Standard.
The syntax of external representations of various kinds of objects
accompanies the description of the primitives for manipulating the
objects.