@ryang I am just ping you to make sure that you saw Xander Henderson's response:

@XanderHenderson "The tools I have tell me that the tag synonym was "renamed" yesterday (I don't really know what that means)." Yes yes, I suppose you and I were both misled by the same "renamed" data point, and I now believe that that so-called renaming actually refers to MY action of trying to tag a post as PL resulting in its immediate automatic retagging/"renaming" as FOL.

The current state of affairs (PL and FOL neither merged nor independent) is very bad: there are many posts tagged PL but not FOL, and currently the MSE search engine won't return them as results (meaning, these posts are harder to get noticed/found) because the system now treats every search for PL as a search for FOL instead. im ok either to merge the two tags or to desynonymise them, but i dont like this limbo status at all.

I have asked some questions related to searching and synonyms: Tag synonyms and searching and What are differences between synonyms with and without merging from the practical point of view?

I'll have to admit that for a long time I was blissfully unaware of the fact that searching for combination of keywords and tags never returns the synonyms; only the master tag.

Compare searching for expressing chain statements with notation, first-order-logic and predicate-logic.

At least such post are returned when searching only with tags: math.stackexchange.com/questions/tagged/…

new-tag A new tag free-lie-algebraa. The name free-lie-algebra was probably intended - the question is whether such a tag is actually useful.