Given a long exact sequence of the form $$ \dots\to A'_n \to B'_n \to C'_n \,\xrightarrow{\omega_n}\, A'_{n-1} \to B'_{n-1} \to C'_{n-1}\to \dots\qquad (*) $$ is there a way to recover a short exact sequence of complexes $\mathcal A=\{A_n,\partial_n^A\}$, $\mathcal B=\{B_n,\partial_n^B\}$, $\mathcal C=\{C_n,\partial_n^C\}$ such that the sequence (*) "is" the long exact sequence in homology induced by $$ 0\to \mathcal A\to \mathcal B\to \mathcal C \to 0 $$ and the morphisms $\omega_n$ are in fact the connection morphisms of that homology? I mean $A'_n\cong H_n(\mathcal A)$ for all $n\ge 0$ and similarly for $B'_n$, $C'_n$.

I expect the answer will be "obviously no", but then is there a case in which it is possible?


This is not a direct answer, but related. This paper by Jan Stovicek addresses the question "which long exact sequences can arise from the snake lemma" so it might be of help here.


  • $\begingroup$ Jan's name is Jan :) $\endgroup$ – Mariano Suárez-Álvarez Dec 9 '10 at 1:36
  • $\begingroup$ @Mariano: Sorry, it was a typo. Fixed. $\endgroup$ – Timothy Wagner Dec 9 '10 at 1:49

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