Spokojnie możemy powtórzyć każdy auxiliary verb, nie tylko 'do':
1. I wouldn't mind a coffee. Neither would I?
2. Zależy, co mamy na myśli:
So did I = I liked the company, too
Neither could I = I couldn't stand him, either.
3. One of the men was a bit unfriendly, and so was the woman.
4. You're next, aren't you? - it's a question tag, isn't it?
5. I'll go... So will I.