《论衡·卷二十九·对作篇》
周文王把八卦画出来，自己推演成六十四卦，所以称为推衍，说《论衡》的写成，像推演六十四卦一样，但又不是如此。
文王图八，自演为六十四，故曰衍。谓《论衡》之成，犹六十四卦，而又非也。
King Wen of Zhou drew out the eight trigrams and himself extrapolated them into sixty-four hexagrams, so it is called extrapolation. To say that <Lunheng> is written like the extrapolation of the sixty-four hexagrams, however, is not so.