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Let's consider the next theorem.

Theorem [The cohomology Leray-Serre Spectral sequence] Let $R$ be a commutative ring with unit. Given a fibration $F\hookrightarrow E\overset{p}{% \rightarrow }B$, where $B$ is path-connected, there is a first quadrant spectral sequence of algebras $\left\{ E_{r}^{\ast ,\ast },d_{r}\right\} $, with \begin{equation*} E_{2}^{p,q}\cong H^{p}\left( B;\mathcal{H}^{q}\left( F;R\right) \right) \end{equation*} and converging to $H^{\ast }\left( E;R\right) $ as an algebra, where $% \mathcal{H}^{q}\left( F;R\right) $ denotes the cohomology of $B$ with local coefficients in the cohomology of $F$, the fiber of $p$. Furthermore, this spectral sequence is natural with respect to fiber-preserving maps of fibrations. I want to calculate \begin{equation*} E_{2}^{p,0}\cong H^{p}\left( B;\mathcal{H}^{0}\left( F;R\right) \right) \end{equation*} Some sources claim that if $F$ is path-connected, then the local coefficients system $\mathcal{H}% ^{0}\left( F;R \right) $ over $B$ (here $R$ is a principal ideal domain, I don't know if the question has anything to do with this) is trivial and \begin{equation*} E_{2}^{p,0}=H^{p}\left( B;\mathcal{H}^{0}\left( F;R \right) \right) =H^{p}\left( B;H^{0}\left( F;R \right) \right) =H^{p}\left( B;R \right) \end{equation*} First of all, I'm curious about the proof of this, that is why the local coefficients system $\mathcal{H} ^{0}\left( F;R \right) $ over $B$ is trivial.

Secondly, is the path connectedness of $F$ related to the cohomology used?

I know that in the case of singular cohomology, $H^{0}\left( X;R\right) =R$ if and only if $X$ is path-connected, and in the case of Alexander-Spanier cohomology, $H^{0}\left( X;R\right) =R$ if and only if $X$ is connected.

So, If I use the Alexander-Spanier cohomology instead of the singular cohomology, is it enough for $F$ to be connected?

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    $\begingroup$ You can think of $H^0(F;R)$ as functions $\pi_0(F)\to R$, and $\pi_1(B)$ acts by pre-composing with the action of $\pi_1(B)$ on $\pi_0(F)$. If $F$ is path-connected this action is clearly trivial. $\endgroup$
    – Mark Grant
    Commented Nov 28, 2023 at 13:40
  • $\begingroup$ I don't know about Alexander-Spanier cohomology, but presumably replace $\pi_0(F)$ with the set of connected components in the above comment. $\endgroup$
    – Mark Grant
    Commented Nov 28, 2023 at 13:40
  • $\begingroup$ @MarkGrant Can you write more clearly this action? $\endgroup$ Commented Nov 30, 2023 at 19:13
  • $\begingroup$ It is induced by the standard action map $\Omega B\times F\to F$ which comes from the homotopy lifting property, as described in many textbooks e.g. Hatcher's Algebraic Topology, Chapter 4. $\endgroup$
    – Mark Grant
    Commented Dec 1, 2023 at 10:11
  • $\begingroup$ @MarkGrant The local coefficients system is given by $\pi_1 (B) \rightarrow Aut (H^0(F))$. So It seems to me that path connectedness of $F$ is related to the cohomology used. Am I wrong? $\endgroup$ Commented Dec 5, 2023 at 8:49

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