4.1.2.4 Atoms

An atom is identified by its name, which is a sequence of up to 65535 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. Backslashes in the sequence denote escape sequences (see ref-syn-syn-esc), and if the single quote character is included in the sequence it must be escaped, e.g. 'can\'t'.
• 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) as an alternative to .(X,[]), 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.