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Aug 21, 2021 at 0:40 comment added dvitek Note that Yamada-Vogel will also work in case (2). But in case (1) the Yamada-Vogel algorithm necessarily introduces negative crossings. I don't know of any techniques that can bound the "positive braid index" or "positive braid length" of a positive knot in terms of its crossing number.
Aug 20, 2021 at 16:09 vote accept Hauke Reddmann
Aug 20, 2021 at 15:45 comment added dvitek Question (3) can be answered in the ordinary case by stepping through a proof of Alexander's theorem, which actually constructs a braid representative. I think you'll have a somewhat easier go of it if you look into the Yamada-Vogel algorithm; see section 2.2 of Birman-Brendle, "Braids: a survey" for a good overview. In particular I believe you can get a quadratic-in-the-crossing-number bound without working too hard.
Aug 20, 2021 at 14:03 history edited Sam Nead CC BY-SA 4.0
phrasing
Aug 20, 2021 at 12:35 history edited Sam Nead CC BY-SA 4.0
Hmmm
Aug 20, 2021 at 12:23 history edited Sam Nead CC BY-SA 4.0
added ref.
Aug 20, 2021 at 12:03 history answered Sam Nead CC BY-SA 4.0