Variables may be written as any sequence of alphanumeric characters (including _) beginning with either a capital letter or _. For example:

     X   Value   A   A1   _3   _RESULT

If a variable is referred to only once in a clause, it does not need to be named and may be written as an anonymous variable, represented by the underline character _ by itself. Any number of anonymous variables may appear in a clause; they are read as distinct variables. Anonymous variables are not special at runtime.