Date/Time
Date(s) - 05/02/2026
3:30 pm - 4:30 pm

Speaker: Duncan McCoy (UQAM)

Location: Hamilton Hall, Room 312

Title: The unknotting number of positive alternating knots

Abstract: The unknotting number is simultaneously one of the simplest classical knot invariants to define and one of the most challenging to compute. This intractability stems from the fact that typically one has no idea which diagrams admit a collection of crossing changes realizing the unknotting number for a given knot. For positive alternating knots, one can show that if the unknotting number equals the lower bound coming from the classical knot signature, then the unknotting number can be calculated from an alternating diagram. I will explain this result along with some of the main tools in the proof, which are primarily from smooth 4-dimensional topology. This is joint work with Paolo Aceto and JungHwan Park.