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Questions about the branch of algebra that deals with groups.

54 votes
Accepted

Do all exact $1 \to A \to A \times B \to B \to 1$ split for finite groups?

This is true (1). It was extended to finitely generated profinite groups here (2). Surprisingly, it is also true in the category of finitely generated modules over a Noetherian commutative ring (3). …
LSpice's user avatar
  • 12.9k
1 vote
1 answer
895 views

Torsion-free and torsionless abelian groups

This question is motivated by my most spectacular answer on MO (: Let $A$ be a module over $\mathbb Z$. $A$ is said to be torsion-free if $na=0$ implies $n=0$ or $a=0$ for any $n\in \mathbb Z, a\i …
14 votes

Zero divisor conjecture and idempotent conjecture

Clearly one implies the other as $x^2=x$ means $x(x-1)=0$. I doubt they are known to be equivalent since the sources I found: the K-theory handbook and Alain Valette survey (see Conjecture 2) listed …
Hailong Dao's user avatar
  • 30.6k
16 votes

The finite subgroups of SL(2,C)

Dolgachev has a note on the McKay correspondence in dimension $2$. It has a lot of cool stuff on subgroups of $SL(2,\mathbb C)$, mostly from the algebraic geometry point of view.
Hailong Dao's user avatar
  • 30.6k