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Jun 2, 2022 at 15:36 comment added user483320 Thank you very much!
Jun 2, 2022 at 15:33 comment added Maxime Ramzi @user483320 : yes, exactly ! And by covering theory, the category of $\pi_1(S^1)$-sets is equivalent to the category of covers of $S^1$, which is something you can access geometrically (for instance by finding the universal cover, $\mathbb R$, or by using $S^1= [0,1]/(0=1)$
Jun 2, 2022 at 15:29 comment added user483320 How do you calculate $\pi_1(S^1)$ using the fundamental theorem of covering spaces? If by "the knowledge that you can recover π1 from the category of π1-sets" you mean that whenever G-set and H-set are equivalent categories, then G is isomorphic to H -- so can we calculate $\pi_1(S^1)$ by proving that the category of $\pi_1(S^1)$-sets is equivalent to the category of $\mathbb Z$-sets, is that what you are saying?
May 9, 2022 at 18:11 history answered Maxime Ramzi CC BY-SA 4.0