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: 
**Proposal: make [smooth-manifolds](https://math.stackexchange.com/questions/tagged/smooth-manifolds "show questions tagged 'smooth-manifolds'") a synonym of [manifolds](https://math.stackexchange.com/questions/tagged/manifolds "show questions tagged 'manifolds'").**

In theory, there is a distinction between these tags, with [smooth-manifolds](https://math.stackexchange.com/questions/tagged/smooth-manifolds "show questions tagged 'smooth-manifolds'") referring to just differentiable manifolds and [manifolds](https://math.stackexchange.com/questions/tagged/manifolds "show questions tagged 'manifolds'") also including topological manifolds. In practice, the distinction does not matter for many questions and [manifolds](https://math.stackexchange.com/questions/tagged/manifolds "show questions tagged 'manifolds'") alone is very frequently used for questions that are actually only about smooth manifolds. For example, looking at the 10 most recent [manifolds](https://math.stackexchange.com/questions/tagged/manifolds "show questions tagged 'manifolds'") questions, 8 of them seem to be primarily or entirely about smooth manifolds but only 3 of them are also tagged [smooth-manifolds](https://math.stackexchange.com/questions/tagged/smooth-manifolds "show questions tagged 'smooth-manifolds'"). If you want to use tags to signal that you are interested specifically in smooth manifolds, there are also other ways to do so, for instance using [differential-topology](https://math.stackexchange.com/questions/tagged/differential-topology "show questions tagged 'differential-topology'") or [differential-geometry](https://math.stackexchange.com/questions/tagged/differential-geometry "show questions tagged 'differential-geometry'").
**Proposal: pluralise [alternative-proof](https://math.stackexchange.com/questions/tagged/alternative-proof "show questions tagged 'alternative-proof'")**.

Reasons:

1. It's a convention to have pluralised tag names if possible.
2. A proposition sometimes has multiple proofs.