Surgery on a knot in (Surface x I)
Abstract
Suppose F is a compact orientable surface, K is a knot in F x I, and N is the 3-manifold obtained by some non-trivial surgery on K. If F x 0 compresses in N, then there is an annulus in F x I with one end K and the other end an essential simple closed curve in F x 0. Moreover, the end of the annulus at K determines the surgery slope. An application: suppose M is a compact orientable 3-manifold that fibers over the circle. If surgery on a knot K in M yields a reducible manifold, then either: the projection of K to S1 has non-trivial winding number; or K lies in a ball; or K lies in a fiber; or K is a cabled knot.
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