Atoms

An atom is identified by its name, which is a sequence of up to 65532 characters (other than the null character). An atom can be written in any of the following forms:

• Any sequence of alphanumeric characters (including _), starting with a lowercase letter. Note that an atom may not begin with an underscore.
• Any sequence from the following set of characters (except /*, which begins a comment):

            + - * / \ ^ < > = ` ~ : . ? @ # $ &
            

• Any sequence of characters delimited by single quotes, such as:

            'yes'  '%'
            

  If the single quote character is included in the sequence it must be written twice, for example:

             'can''t'  ''''
            

  For further details see ref-syn-syn-nte.

• Any of:

            ! ; [] {}
            

  Note that the bracket pairs are special: [] and {} are atoms but [, ], {, and } are not. The form [X] is a special notation for lists (see ref-syn-cpt-lis), and the form {X} is allowed as an alternative to {}(X).

Examples of atoms are:

     a   void   =   :=   'Anything in quotes'   []
     

WARNING: It is recommended that you do not invent atoms beginning with the character $, since it is possible that such names may conflict with the names of atoms having special significance for certain built-in predicates.