书籍经过多次传抄，“鱼” 字可能写成 “鲁” 字，“虚” 字可能写成 “虎” 字。

Mathematics is not a deductive science—that's a cliché. When you try to prove a theorem, you don't just list the hypotheses and then start to reason. What you do is trial and error, experimentation, guesswork.