On Extension of Coverings
نویسندگان
چکیده
We address the question of when a covering of the boundary of a surface F can be extended to a covering of the surface (equivalently: when is there a branched cover with a prescribedmonodromy ). If such an extension is possible, when can the total space be taken to be connected? When can the extension be taken to be regular? We give necessary and sufficient conditions for both finite and infinite covers (infinite covers are our main focus). In order to prove our results, we show group-theoretic results of independent interests, such as the following extension (and simplification) of the theorem of Ore [22]: every element of the infinite symmetric group is the commutator of two elements which, together, act transitively.We also make some general remarks on writing elements of various groups as commutators.
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