在 请教肖子 中请教的问题，看来还是肖子的答复【7】比较靠谱：x*m<1. 也许可以作为a rule of thumb，来判断这是否可以忽略二次以上高阶项？

所谓rule of thumb，好像没有什么好的汉译，意思是a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination.

本来指望曹大侠发表高见的。曹大侠不发话，那就取名“肖子粗判法”吧，曹大侠也许可以帮忙审一下是否原创。