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Am I right that a vector bundle $(E,M)$ of rank 0 means that sections of $E$ are functions $f:M \to M$?

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    Sorry I don't get how I can use that $\Pi \circ S = id_M $ for a section $S$. All I know is that $S\circ d:M \to M$ where $d$ is the said diffeomorphism.2012-12-02

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If $E$ is a rank $0$ vector bundle over $M$, identify $E \cong M\times\{0\}$. The projection map $\pi:E\to M$ is projection onto the first factor of the product. Every section of $E$ is a map $s:M\to E$ such that $\pi\circ s = id_M$.

With these three facts, you can completely characterize every single section of $E$ by asking what sort of function $M\to M\times\{0\}$ composed with projection to $M$ gives the identity on $M$.

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    The empty basis is a global trivialization of $E$, so we can identify $E$ with the product bundle $M\times\{0\}$.2012-12-04