On the Construction of Branched Coverings of Low-Dimensional Manifolds

Abstract
Several general results are proved concerning the existence and uniqueness of various branched coverings of manifolds in dimensions 2 and 3. The results are applied to give a rather complete account as to which 3-manifolds are branched coverings of , , , or the nontrivial -bundle over , and which degrees can be achieved in each case. In particular, it is shown that any closed nonorientable 3-manifold is a branched covering of of degree which can be chosen to be at most 6 and with branch set a simple closed curve. This result is applied to show that a closed nonorientable 3-manifold admits an open book decomposition which is induced from such a decomposition of .
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