as: Symbol Intro
3.4 Symbols
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A "symbol" is one or more characters chosen from the set of all letters
(both upper and lower case), digits and the three characters '_.$'. On
most machines, you can also use '$' in symbol names; exceptions are
noted in 
Machine Dependencies. No symbol may begin with a
digit. Case is significant. There is no length limit; all characters
are significant. Multibyte characters are supported. Symbols are
delimited by characters not in that set, or by the beginning of a file
(since the source program must end with a newline, the end of a file is
not a possible symbol delimiter). Symbols.
Symbol names may also be enclosed in double quote '"' characters. In
such cases any characters are allowed, except for the NUL character. If
a double quote character is to be included in the symbol name it must be
preceeded by a backslash '\' character.
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