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<p class="MsoNormal"><span style="font-size:11.0pt">Happening in 20 mins!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="color:black">From: </span></b><span style="color:black">"Rot, T.O." <t.o.rot@vu.nl><br>
<b>Date: </b>Friday, 1 April 2022 at 09:59<br>
<b>To: </b>"_list_topology.beta" <topology.beta@listserver.vu.nl><br>
<b>Cc: </b>"Vorst, R.C.A.M. van der" <r.c.a.m.vander.vorst@vu.nl>, "Fabert, O." <o.fabert@vu.nl>, "Roos Hoefgeest, P.E.R." <p.e.r.rooshoefgeest@vu.nl><br>
<b>Subject: </b>Re: Friday DDT&G<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">Dear all,</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">This is happening today.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Best,</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Thomas</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
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<p class="MsoNormal"><b><span style="color:black">From: </span></b><span style="color:black">"Rot, T.O." <t.o.rot@vu.nl><br>
<b>Date: </b>Tuesday, 29 March 2022 at 15:40<br>
<b>To: </b>"_list_topology.beta" <topology.beta@listserver.vu.nl><br>
<b>Cc: </b>"Vorst, R.C.A.M. van der" <r.c.a.m.vander.vorst@vu.nl>, "Fabert, O." <o.fabert@vu.nl>, "Roos Hoefgeest, P.E.R." <p.e.r.rooshoefgeest@vu.nl><br>
<b>Subject: </b>Friday DDT&G</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">Dear all,</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">This friday there is the DDT&G. This starts at 14:00 in the union/intersection/mathlab. The speaker is Stefan Behrens about Freedman's disk embedding theorem and the topology of 4-manifolds.
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<span style="font-size:9.0pt;font-family:Helvetica;color:black">Schedule</span><o:p></o:p></h5>
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<span style="font-size:9.0pt;font-family:Helvetica;color:black">14:00-15:00: First part of the minicourse<br>
15:30-16:30: Second part of the minicourse</span><o:p></o:p></p>
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<span style="font-size:9.0pt;font-family:Helvetica;color:black">Abstract</span><o:p></o:p></h5>
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<span style="font-size:9.0pt;font-family:Helvetica;color:black">Freedman's disk embedding theorem is a cornerstone of 4-manifold topology. In order to appreciate the result, one has to be aware that manifold topology is divided into low and high dimensions.
The border runs somewhere in dimension 4. The high dimensional world has powerful tools to tackle classification problems for manifolds, known as surgery theory and the s-cobordism theorem. A key feature of high dimensional manifolds is the Whitney trick,
which allows to make certain geometric and algebraic intersection counts match. Unfortunately, the standard Whitney trick is not available in dimension 4 and it is known that the high-dimensional machinery does not apply to smooth 4-manifolds. In contrast,
Freedman's theorem makes the Whitney trick available for a class of topological 4-manifolds (including all simply connected ones), thereby opening the gates for surgery and s-cobordism techniques. The goal of the minicourse is to explain the statement of the
disk embedding theorem, to indicate why it is important, and to give at least a rough idea of the proof.</span><o:p></o:p></p>
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<span style="font-size:9.0pt;font-family:Helvetica;color:black">See this <a href="https://www.quantamagazine.org/new-math-book-rescues-landmark-topology-proof-20210909/">Quanta magazine article about the book Stefan coauthored about this topic.</a></span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Bring your (master) students along!
</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">We’ll have drinks afterwards. I will go out for dinner with the speaker to pizzalab. Let me know if you want to join asap.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Best,</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Thomas</span><o:p></o:p></p>
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