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Jun 11, 2020 at 7:39 comment added A beginner mathmatician @fierydemon. I think much simpler argument avoiding covering groups exists. Consider the map $(g,h)\mapsto gh$ from $(Z_G)_0\times G_{ss}$ to $(Z_G)_0G_{ss}.$ The derivative of this map is clearly onto and hence an isomorphism as the corresponding Lie algebras have the same dimension. Thus the map is local diffeomorphism. As the exponential map is a local diffeomorphism and $G$ is connected. The map $(g,h)\mapsto gh$ is surjective.
Jun 8, 2020 at 0:56 comment added Ryan Hendricks You might argue along the lines that $\widetilde{G_{ss}}\times \widetilde{(Z_G)_0}$ is a covering group of $(Z_G)_0 G_{ss}$, that $(Z_G)_0 G_{ss}\subset G$, and $G$ cannot be any bigger than $(Z_G)_0 G_{ss}$ and still have $\widetilde{G_{ss}}\times \widetilde{(Z_G)_0}$ as a covering group
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Jun 9, 2020 at 18:52
Jun 7, 2020 at 19:16 history edited YCor CC BY-SA 4.0
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Jun 7, 2020 at 19:10 history asked A beginner mathmatician CC BY-SA 4.0