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Martin Sleziak
Martin Sleziak
2:39 AM
2
A: On the top-level tag ra.rings-and-algebras

Gerhard PasemanHow synchronized/copacetic/friendly do we want MathOverflow and ArXiv to be? I can put up an argument for keeping the status quo (new users will identify the two tag systems, researchers in structure theory will look under the ra tag as well as other pertinent tags, other users will use the ArXi...

In case it helps somebody else who was looking for it, here is link to descriptions of arXiv categories: arxiv.org/archive/math
I suppose in many cases the tag-excerpt was directly taken from there. At least it seems to be case for ra.rings-and-algebras‌​: "Non-commutative rings and algebras, non-associative algebras, universal algebra and lattice theory, linear algebra, semigroups"
The link is also included in this answer:
17
A: Why are MO tags formatted as they are?

user9072The tags with a two-letter prefix are exactly those tags that correspond to a math subject class on arXiv. They serve as top-level tags. As a rule, each question should have at least one of these top-level tags. The formatting is mainly in place to distinguish them from usual tags; that it can ...

Since I have mention the post - some tags mentioned there were renamed (without synonym) which means that the corresponding links are not working at the moment:
Oct 29 '17 at 19:01, by Martin Sleziak
As a result, on some places we have links to empty tags, such as in Frequently asked questions about tagging on MathOverflow or Why are MO tags formatted as they are?
 

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