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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.

7 votes
0 answers
225 views

Phantom category with trivial Hochschild cohomology

An admissible subcategory $C\subset D$ of a triangulated category is called phantom if $K_0(C)=0$. Such categories may be detected by their Hochschild cohomology (but usually have trivial Hochschild h …
evgeny's user avatar
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4 votes
0 answers
349 views

How should one understand shifted Lie algebras, like $T_X[-1]$?

Let $X$ be an algebraic variety, $at(E) \in Ext^1(E, E \otimes T)$ the Atiyah class of a complex $E \in D(Coh X)$ (see Markaryan, $\S$1.1-1.2). Then $at(\Omega[1])$ gives a "shifted Lie algebra" on $ …
evgeny's user avatar
  • 1,980
9 votes
1 answer
449 views

Is this sequence of Lie algebra cohomology a part of spectral sequence?

There is an exact sequence $$0 \to H^2(\mathfrak{g}, k) \to H^1(\mathfrak{g}, \mathfrak{g}^*) \to H^0(\mathfrak{g}, S^2\mathfrak{g}) \xrightarrow{d} H^3(\mathfrak{g}, k) \to H^2(\mathfrak{g}, \mathf …
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