I recently came across Andrea Mori's question Explicit Casselman theory: reference needed. The comments 1 2 make reference to matrices rendering poorly, and then being fixed, and I was curious what had changed, so I checked the version history. The relevant version, version 5, seems to have no content. I don't know how to link to the diff (and Meta.SE suggests it's not possible), but, if you click the drop down on the relevant revision on the version history, then you'll notice that … nothing happens, or, rather, the diff appears to be empty. How did an edit that must have had content just disappear?
A few comments which might be useful for somebody who could be in the mood to try to investigate this a bit more - I am basically summarizing the things already mentioned in comments or in chat.
- For the post mentioned in the question, here are the SEDE queries showing the texts of all revisions and the comparison of the two relevant revisions.
- If you check the revision history of this answer - more specifically revision 2 - it looks a bit similar. The edit summary says "Fixed LaTeX" - but there is no change. And
\*can be seen in the older revisions of this post, too. Again, you can get from SEDE the bodies of all revisions and the comparison of the two revisions.
One can try to find some other similar edits - but in doing so, you'll probably find that edits which appear to change nothing are relatively common. Regarding the SEDE queries that I posted here, you should take into account both the fact that I am not really that experienced with SQL and also some peculiarities in how SQL compares strings.1
- This query finds revisions which did not change the length - but various fixes which replace some character by a different one are probably among relatively common types of edits. So it's no surprise that there are plenty of such edits.
- This is a bit more relevant - no change in the body. SEDE returns 948 such edits.
- One can try to find such edits by a specific user: LSpice, Martin Sleziak. (I have included these two users as examples. The query is mentioned in case you're curious whether some of your edits are of this type - simply replace the userid parameter by your id.2)
- Many of those edits say "Edit removed during grace period" in the edit summary - one can omit such edits, you will still get 658 results.
- Specifically to this question, one can check whether
\*appears in the text of the old revision or of the new revision. This is how I found the answer mentioned above.
- One of the comments speculated that all instances of
\*have been removed - but this is not the case. SEDE returns 152 posts with
\*. This includes
\\*which can appear, for example, in a matrix. When searching for posts with
\\*, I get 145 results. There are 180 posts where
1Stack Overflow: SQL - string comparison ignores space
2Meta Stack Exchange: What is my user ID?