1． 在if引起的从句中如有等词倒装时，省略if。
Were I you, I would not do it.
Had we known your telephone number, I would have given you a phone call.
2．
We have finished our homework, so have they. (= and they have finished their homework , too)
If you don't go to the concert, neither shall I. (= I shall not go to the concert either)
