[拓樸] universal covering

[Babbage (驕傲體現於健忘)]

請問universal covering map是不是一定regular?
或者一般而言, 在什麼條件下, 一個covering map會是regular呢?
感謝~

備註:
universal covering map p: M->N
regular的定義是 for all x in N and a,b in p^-1(x), there
                exist a (unique) covering transformation
                f:M->M such that f(a)=b.

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