# Changing the question and invalidating previous answer.

I know that this is a common problem, one very much discussed in meta. But what I want to know is if I made a good call in this particular instance.

I posted this question a few minutes ago on MSE. However, I made a blunder. I forgot fundamental assumptions for the question (essentially, the hypothesis of Mayer-Vietoris).

Previous to my update, an answer to the question as posed was submitted. It was (then) correct, and I have upvoted it. However, it was not correct to deal with the question I wanted.

The problem is: the context I gave (explicitly talking about Mayer-Vietoris) implicitly states that I am working on the assumptions that it makes. This made me think that the question was not intrinsically badly posed and misleading, so I decided not to delete it and simply state things explicitly.

But of course, it was my error not to put everything explicitly. Therefore, I left the previous answer upvoted and accepted another one.

Was this the best path in this situation, or was it better to follow another course of action? (As of now, the previous answer explains very well what was the situation, so I think the outcome was not bad. But I would like to know people's opinions, since I don't like the situation of "changing the question while invalidating answers").

• Why not ask a second question (and think more about the question you really want to ask, next time)?
– Did
Mar 13 '17 at 9:32
• @Did Because of the fourth paragraph I wrote. If I had not mentioned any context, I would ask a second question. But given that I did, I think it would be "artificial" (for lack of a better word) to post another question.
– Aloizio Macedo Mod
Mar 13 '17 at 11:00
• This paragraph does not change the fact that the first version of your question was (rightfully, according to you) interpreted differently. If the first answer posted was indeed addressing the question as it was written at the time, I see no reason to invalidate this answer. And a convenient way (to which I see zero defect, to be frank) to avoid this, is to post another question.
– Did
Mar 13 '17 at 11:06