Here are the *closed* questions tagged (at this date) with the deprecated [tag:abstract-algebra]. 

https://mathoverflow.net/questions/150660/finite-index-self-normalizing-subgroup-of-f-2


https://mathoverflow.net/questions/204802/why-do-we-not-lose-any-generality-by-proving-it-only-for-finitely-generated-grou

*(not closed but downvoted)* https://mathoverflow.net/questions/225240/group-associated-to-the-monoid-cal-px-times-x-circ

https://mathoverflow.net/questions/215946/making-idempotent-element-by-a-relation

https://mathoverflow.net/questions/221059/how-to-solve-this-system-of-equations

https://mathoverflow.net/questions/312934/how-to-show-the-set-operatornamehom-kl-bark-of-all-k-embeddings-of

https://mathoverflow.net/questions/191629/is-the-algebraic-closure-of-the-quaternions-finite-dimensional

https://mathoverflow.net/questions/218963/is-there-any-construction-of-infinite-dimensional-algebraic-division-ring

https://mathoverflow.net/questions/216392/polynomial-constraints-triggered-by-irreducibility

https://mathoverflow.net/questions/144341/does-this-solution-guarantee-deta-0-where-a-in-mr

https://mathoverflow.net/questions/223187/is-k-cap-langle-h-cup-n-rangle-subseteq-langle-h-cup-k-cap-n-rangle

https://mathoverflow.net/questions/248988/properties-of-colon-ideal

https://mathoverflow.net/questions/129514/diagonalize-the-simultaneous-matrices-and-its-background

https://mathoverflow.net/questions/28684/learning-algebra-group-theory-on-my-own

**now deleted** https://mathoverflow.net/questions/47534/unit-ideal-in-non-commutative-rings

**now deleted** https://mathoverflow.net/questions/157122/algebra-generated-by-a-tree-edit

**now deleted** https://mathoverflow.net/questions/127611/an-exercise-about-tor

**now deleted** https://mathoverflow.net/questions/266080/does-alexander-whitney-formula-imply-pythagoras-theorem