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Apr 22, 2022 at 23:39 comment added Ryan Budney @Echo: okay I think I see how to assemble an argument using your sketch. You really have to hit the problem over the head with a lot of 3-manifold theory. But I think there is an argument there. Unfortunately it's not the kind of organic argument I was hoping for.
Apr 22, 2022 at 23:37 history edited Ryan Budney CC BY-SA 4.0
flesh out the strategy described by Echo in the comments.
Apr 22, 2022 at 7:54 comment added user473423 Right, I overlooked that. So let's say you assume additionally, that your knot admits a diagram with finitely many crossings (maybe that's automatically true), but then I guess you can modify the usual process of constructing a Seifert surface in a way that you get a smooth surface outside an arbitrary small neighbourhood U of the knot. You can iterate this process to get ever closer to the knot and at the same time make the surfaces agree outside a somewhat bigger neighbourhood. That menas, they will converge to a Seifert surface which is smooth in the interior.
Apr 22, 2022 at 7:26 comment added Ryan Budney Certainly there are smoothing processes that involve convolution, but I do not see one available in this circumstance. One of the main problems with convolution-type arguments is they tend to not preserve functions being embeddings.
Apr 22, 2022 at 7:18 comment added user473423 You can smoothen a given Seifert surface by convolution. If you make the function, you convolve with, dependent on the distance to the boundary, you get the result you want.
Apr 22, 2022 at 5:13 history asked Ryan Budney CC BY-SA 4.0