A symbol is either a string of alphanumeric characters and underscores and periods beginning with a letter or a digit or an underscore or it is a string of printable ascii characters enclosed in double quotes. Note that, in the current implementation, there is no way of escaping double quotes in quoted strings. Note also that it is common practice not to use upper case letters in symbols except as the first character. (This is to allow interoperation to implementations that are case-independent and, therefore, do not distinguish upper and lower case letters).

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