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Commutative rings, modules, ideals, homological algebra, computational aspects, invariant theory, connections to algebraic geometry and combinatorics.

1 vote
0 answers
631 views

when is a sum of idempotents idempotent in commutative ring theory?

As this question demonstrates that the sum of idempotents is idempotent iff every pairwise product is zero, for finite matrices with complex entries. What additional restrictions do we need to put i …
Mozibur Ullah's user avatar
10 votes
2 answers
1k views

why are subextensions of Galois extensions also Galois?

Generally a Galois extension is defined to be an algebraic extension that is also normal & separable. It is then shown that in the sequence of field extensions $L|M|K$ if $L|K$ is Galois then $L|M$ is …
Mozibur Ullah's user avatar