诸如prolog、Mercury、SQL、XSLT这样的语言、ebnf语法和各种格式的真正配置文件，都声明某事是这种情况，或者应用了某些约束。
Languages like Prolog, Mercury, SQL, XSLT, EBNF grammars, and indeed configuration files of various formats, all declare that something is the case, or that certain constraints apply.
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