Question in the appendixes A of O'Neill book 2

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I'm reading appendixes A of O'Neill's book, "Semi-riemannian geometry" and I don't understand a something.

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Where we use the assumption that $P$ is simply connected?

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The assumption that $P$ is simply connected shows up when you show that that $\tilde{\phi}$ is a well defined continuous function.

Try it out when $\tilde{M} = \mathbb{R}, M = S^1$, and $P = S^1$ where the map $\tilde{M}\rightarrow S^1$ is the usual universal covering, and $P\rightarrow M$ is the identity.

Then the lift of the identity is discontinuous.