I recently asked two questions: Simultaneous coset spaces and Manifolds as simultaneous coset spaces which appear to be quite similar. The first was closed as 'not research-level mathematics' while the second was not. I assume this means that the first question is too trivial for this site and the second one is not (or has not yet been identified as such).

I am a research mathematician and both questions arose during my research, so both questions meet following help centre criteria:

- the sorts of questions you come across when you're writing or reading articles or graduate level books (I did)
- your question is of interest to at least one other mathematician (it is trivial and therefore has been solved by another mathematician).
- questions that actually have a specific answer

I suspect that something else is meant by 'not research-level' in this case. It seems it could be any of the following:

- There are some mathematicians on this site who know the answer already.
- The answer would be obvious to all mathematicians working in the area (I do not work in this field and it arose in a different context).
- A mathematician working in any area would know the answer (I don't believe this is the case).

Could somebody explain which (if any) of these is the correct reason?