1.2.1 Atoms

An atom is either:

1. A string of characters made up of upper-case letters, lower-case letters, digits, and the underscore character, that begins with a lower-case letter. For example: butch, big_kahuna_burger, and m_monroe2.

2. An arbitrary sequence of character enclosed in single quotes. For example 'Vincent', 'The Gimp', 'Five_Dollar_Shake', '&^%&#@$ &*', and ' '. The character between the single quotes is called the atom name. Note that we are allowed to use spaces in such atoms --- in fact, a common reason for using single quotes is so we can do precisely that.

3. A string of special characters. For example: @= and ====> and ; and :- are all atoms. As we have seen, some of these atoms, such as ; and :- have a pre-defined meaning.