$$ Lexicon-File ::= {Constant-Definition | Constant-Expression ";"} .
A lexicon file has the suffix `` .lex''. It consists of any number of values and constant definitions, each terminated by a semicolon. Each value stands for a lexical entry. A value may contain named constants and the operators ``.'', ``+'', ``-'', ``*'', and ``/''. values, the lexical entries; The format of the lexical entries is free, although it should be consistent with the conception of the whole rule system.