I'm confused about the scope of the ra.rings-and-algebras The problem is related to the ambiguity of the word "algebra", which essentially has two (rough) meanings

the meaning "ring", in its various meanings where one has one addition and one multiplication with some reasonable axioms, and possible elaborations and over-structures, notably coming from operator algebras or homological algebra,

the meaning of algebra in the more general framework of universal algebra, including, for instance, semigroups (explicitly mentioned in the current wiki of the tag).

The current wiki for ra.rings-and-algebras basically says that both interpretations are correct, which makes this top-level tag somewhat clumsy.

Each meaning has its own interest and is related to other tags: the meaning (1) is closely related to the more specific tags: ac.commutative-algebra, noncommutative-algebra, homological-algebra, oa.operator-algebras, lie-algebras, qa.quantum-algebra, just to mention the more used. This is not a problem, they can be used in combination (although ra.rings-and-algebras is unnecessary for most question of commutative algebra, since the latter is a quite well-defined area).

The meaning (2) is closely related to universal-algebra, to the deprecated tag abstract-algebra, and not unrelated to ct.category-theory.

The main problem, in my opinion, is the discrepancy between the current wiki of ra.rings-and-algebras and its usage. Namely, looking at the last 200 questions tagged with ra.rings-and-algebras, only about 15 of them pertain to (2), and among these 15, about 11 also pertain to (1) (typically, around embeddings of semigroups in multiplicative semigroups of rings). Among this 15, a single one is not about semigroups.

In the same period (the last 200 questions of ra.rings-and-algebras mean since May of 2017, until now, February 2018), there were 90 questions tagged at least one of universal-algebra, semigroups monoids

Although these numbers are subject to a few minor errors or subjective interpretations, it gives the conclusion that the "universal algebra" and "semigroup" aspects, in the use of ra.rings-and-algebras are completely drown.

In consequence, I'm inclined to remove universal algebra and semigroups from ra.rings-and-algebras, and to give better guidelines to people who want to ask questions pertaining to (2).

Note: the role of universal-algebra is somewhat unclear too: if we have question about a specific structure which does not fit into usual structures with tags (groups, rings, etc, or close variants), one of its problems is that people who have questions about this specific structure may simply ignore the notion of universal algebra, and also the wiki "study of algebraic structures and properties *applying to large classes* of such structures" is not really encouraging.

`xx.*`

tags. $\endgroup$ – François G. Dorais♦ Feb 18 '18 at 18:58s" is also used in universal algebra unrelated to rings, whence the ambiguity. $\endgroup$ – YCor Feb 18 '18 at 19:07since probably people will assume it has the same meaning anyway without reading carefully" I have substantiated the opposite claim with statistics. $\endgroup$ – YCor Feb 21 '18 at 22:28shouldbe used with (universal-algebra) or which ones arecurrently being used.In any case, I have tried to give some kind of current usage summary here in chat. $\endgroup$ – Martin Sleziak Apr 2 '18 at 0:38