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6 votes
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Is any abelian category a subcategory of $\mathrm{Ab}^I$?

Observe that $\bigoplus_I : \textbf{Ab}^I \to \textbf{Ab}$ is a conservative exact functor: it is right exact by general nonsense, it preserves monomorphisms (because e.g. $\bigoplus_{i \in I} A_i$ is …
Zhen Lin's user avatar
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14 votes
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Projectives and Injectives in Functor Categories

For each object $c$ in $\mathcal{C}$, let $c^* : [\mathcal{C}, \mathcal{A}] \to \mathcal{A}$ be evaluation at $c$. It is an exact functor, so if a left adjoint $c_! : \mathcal{A} \to [\mathcal{C}, \ma …
Zhen Lin's user avatar
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7 votes
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Why does tensor product in Ab(V) require colimits in V?

It is easy to define the tensor product as being the object that represents the bilinear maps functor, but to prove that tensor products exist requires something extra. If you have free abelian groups …
Zhen Lin's user avatar
  • 15.9k