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Non-commutative rings and algebras, non-associative algebras, universal algebra and lattice theory, linear algebra, semigroups. For questions specific to commutative algebra (that is, rings that are assumed both associative and commutative), rather use the tag ac.commutative-algebra.

21 votes
4 answers
1k views

Can one show the equivalence of the abstract and classical Jordan decompositions for simple ...

The following fact is basic in the theory of complex Lie algebras: Theorem. Let ${\mathfrak g} \subset {\mathfrak gl}_n({\bf C})$ be a simple Lie algebra, and let $x \in {\mathfrak g}$. Let $x = …
Terry Tao's user avatar
  • 114k
17 votes
0 answers
1k views

Relations in a certain Lie algebra

Let ${\mathfrak g}$ be the (real) Lie algebra generated by infinitely many generators $D_i, E_i$ with $i=1,2,3,\dots$ subject to the following relations for any natural numbers $i,j$: \begin{gather*} …
Terry Tao's user avatar
  • 114k
25 votes
2 answers
2k views

What is the name of this relative semidirect product of groups?

We have two well known definitions of the semidirect product $N \rtimes H$ of groups: (Internal semidirect product) We write $G = N \rtimes H$ if $N$ is a normal subgroup of $G$, $H$ is another subg …
Terry Tao's user avatar
  • 114k
32 votes
1 answer
2k views

Is this formal noncommutative power series identity known?

I recently discovered the following cute formal noncommutative power series identity: if $(x_i)_{i \in I}$ is some finite collection of noncommuting variables, then the formal power series $$ 1 + \sum …
Terry Tao's user avatar
  • 114k