Ko Hung, a writer of the Eastern Chin dynasty (317--420), relates the following story: A certain Ko Hsuan, versed in the occult arts, went boating with several young companions who, noticing several dozen fu in his boat, asked him whether they really worked.
有一回十幾個年輕人跟著他乘舟談天，看見舟上有數十枚符籙，好奇問道：「這些符真的靈驗嗎？