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              Abstract
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 New lower bounds on the unknotting number of a knot are constructed from the
 classical knot signature function. These bounds can be twice as strong as previously
 known signature bounds. They can also be stronger than known bounds arising from
 Heegaard Floer and Khovanov homology. Results include new bounds on the Gordian
 distance between knots and information about four-dimensional knot invariants. By
 considering a related nonbalanced signature function, bounds on the unknotting
 number of slice knots are constructed; these are related to the property of
 double-sliceness.
  
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              Keywords
              
                knot, unknotting number, signature
               
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              Mathematical Subject Classification 2010
              
                Primary: 57M25
               
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              Milestones
              
                Received: 10 July 2018
               
              
                Revised: 12 July 2019
               
              
                Accepted: 12 July 2019
               
              
                Published: 17 March 2020
               
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