Question: New year, new tag management thread.

Rules of the game are basically [the same](https://math.meta.stackexchange.com/q/27653/43351):

* Post your suggestion as an answer here if you see
	+ A particularly bad tag (a rule of thumb: «if I can't imagine a person classifying a tag as either interesting or ignored, I'm getting rid of it»),
	+ A tag that should be a synonym of an existing one,
	+ A tag that used for two or more completely unrelated things,
	+ A need to create a new tag;
* Upvote/downvote/comment as your agree/disagree with suggestions, so please post different suggestions in separate answers;
* Wait a couple of days before implementing a suggestion.
* After the problem described in an answer is resolved, please edit it to say so.
* If your tag suggestion exists in a separate question, please provide a link to the question in your suggestion.

See also:

* The [list with pending and approved synonyms](https://math.stackexchange.com/tags/synonyms).
* The [tagging chatroom](http://chat.stackexchange.com/rooms/3740/tagging) for extended discussion on tagging.
* [Last year's thread](https://math.meta.stackexchange.com/q/27653/43351) to look for suggestions that need to be implemented.

Also, note that one may use `[tag:calculus]` for [calculus](https://math.stackexchange.com/questions/tagged/calculus "show questions tagged 'calculus'"), i.e. tags on the main site, and `[meta-tag:discussion]` for [discussion](/questions/tagged/discussion "show questions tagged 'discussion'"), i.e. for tags on the meta site.

Answer: 
[Following an earlier discussion](https://math.meta.stackexchange.com/a/26310/) I approved a synonym [elementary-probability](https://math.stackexchange.com/questions/tagged/elementary-probability "show questions tagged 'elementary-probability'") to [probability](https://math.stackexchange.com/questions/tagged/probability "show questions tagged 'probability'"). Likely down the road a merge will happen. 

The main reasons are:

* we do not separate tags by level, and in this case there even is [probability-theory](https://math.stackexchange.com/questions/tagged/probability-theory "show questions tagged 'probability-theory'") that is an "advanced" tag so that further separation seems not useful.
* the community did over the past two years not use that tag much. In absolute numbers usage is not that bad (about 70), but there are thousand times as many question in [probability](https://math.stackexchange.com/questions/tagged/probability "show questions tagged 'probability'") overall. Thus, one could say, it is basically just not used at all.
**Proposal: create "linear-fractional-transformation", and synonymize with [lft](https://math.stackexchange.com/questions/tagged/lft "show questions tagged 'lft'") and [mobius-transformation](https://math.stackexchange.com/questions/tagged/mobius-transformation "show questions tagged 'mobius-transformation'").**

They refer to the same thing in most basic cases.

Tag [lft](https://math.stackexchange.com/questions/tagged/lft "show questions tagged 'lft'") is really hard to notice its exsitence, and it only has 16 questions for almost 6 years.

Here's some [discussion](https://chat.stackexchange.com/transcript/message/49991610#49991610) about this.