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(Co)chain complexes, abelian Categories, (pre)sheaves, (co)homology in various (possibly highly generalized) settings, spectra, derived functors, resolutions, spectral sequences, homotopy categories. Chain complexes in an abelian category form the heart of homological algebra.

4 votes

Spectral sequences: opening the black box slowly with an example

There's a paper of Fadell and Hurewicz (in the Annals, mid 1950's) identifying certain differentials with cap products. I can't recall the precise result.
Jeff Strom's user avatar
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4 votes
1 answer
2k views

Tensor product of spectral sequences?

I'm wondering about a cross product for spectral sequences. I've got an idea, and I wonder if it is written up anywhere, or if it even holds water. Let's start with three spectral sequences, $E, F$ …
Jeff Strom's user avatar
  • 12.5k
4 votes
1 answer
3k views

Notation for algebras

Is there standard notation for (1) exterior algebras (2) free graded commutative algebras (3) divided polynomial algebras ? I've seen (and used) $\Lambda$, $\Gamma$, $\Delta$ etc. used for som …
Jeff Strom's user avatar
  • 12.5k
11 votes

Categories First Or Categories Last In Basic Algebra?

Introductory algebra courses tend to systematically confuse products with coproducts, and more generally, confuse targets with domains. This systematically causes confusion in students (what is the d …
6 votes
1 answer
1k views

Solid rings and Tor

A solid ring is a ring $R$ such that the multiplication $R\otimes_{\mathbb{Z}} R \to R$ is an isomorphism. These were classified by Bousfield and Kan; they are subrings of $\mathbb{Q}$, $\mathbb{Z}/ …
Jeff Strom's user avatar
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8 votes
2 answers
2k views

Splitting of the Universal Coefficients sequence

The really beautiful way to prove the Universal Coefficients theorem, to my taste, is to use the fibration sequence $K(\mathbb{Z}, n) \to K(\mathbb{Z}, n) \to K(\mathbb{Z}/k, n)$ (I'm using $\mathbb …
Jeff Strom's user avatar
  • 12.5k