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                    <div align="center"><big><b><big><br>
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                    <div align="center"><big><b><big>Welcome to the 2021
                            Fall talks of ODTU-Bilkent Algebraic
                            Geometry Seminars</big></b></big><b><br>
                      </b><b> </b><b> </b></div>
                    <b> </b>
                    <div align="center"><i>since 2000</i><br>
                      <b> </b> </div>
                    <div align="center"><b> </b><b> </b><b><b>=================================================================</b>
                      </b><br>
                      <b> </b><br>
                      This week the <a
                        href="http://www.bilkent.edu.tr/%7Esertoz/agseminar.htm"
                        target="_blank">ODTU-Bilkent Algebraic Geometry
                        Seminar</a>  is <b>Online.</b>    <br>
                      <br>
                      <i><font color="#ff00ff">This talk will begin at <u><b>15:40</b></u><u>
                            (GMT+3)</u></font></i><br>
                      <br>
                      <b>=================================================================</b></div>
                    <div align="center"><br>
                      <br>
                      <div align="center"><b><img
                            src="cid:part1.8NLG0pLX.dLIPEAvR@bilkent.edu.tr"
                            alt="image.png" width="410" height="516"> </b><font
                          size="-1"><i> </i></font></div>
                      <div align="center"><font size="-1"><i>Paul
                            Gauguin (1848-1903)<br>
                          </i></font></div>
                      <div align="left"><br>
                        <b><b><font color="#ff0000">Speaker:<font
                                color="#000000"> Sergey Finashin<br>
                              </font></font></b></b></div>
                      <div align="left"><b><b><font color="#ff0000">Affiliation:
                              <font color="#000000">ODTÜ</font><br>
                              Title:<font color="#000000"> Two kinds of
                                real lines on real del Pezzo surfaces
                                and invariance of their signed count<br>
                                 </font><br>
                            </font></b></b></div>
                    </div>
                    <div align="left"><b><b><font color="#ff0000">Abstract:</font></b></b><font
                        color="#ff0000"><font color="#000000"> In his
                          classical treatise on real cubic surfaces,
                          Segre discovered two kinds of real lines which
                          he called elliptic and hyperbolic.<br>
                          <br>
                          His enumeration indicated that the number of
                          hyperbolic is greater by 3 than the number of
                          elliptic ones independently of a real
                          structure on the cubic surface.<br>
                          <br>
                          However this property did not receive a
                          conceptual explanation until recently: in a
                          joint work with V.Kharlamov we interpreted a
                          signed count of lines as a signed count of
                          zeroes of some vector field in a Grassmannian
                          (and so, it is Euler’s number of the
                          corresponding vector bundle).<br>
                          <br>
                          In the current work that I will present, we
                          develop an alternative approach to counting
                          lines on real del Pezzo surfaces X of degrees
                          1 and 2 (a projective plane blown up at 8 or 7
                          generic points, respectively).  The two types
                          of real lines are distinguished by certain
                          canonical Pin-structure on the real locus X_R
                          (this looks different from the approach of
                          Segre, but is equivalent to it in the case of
                          cubic surfaces).<br>
                          <br>
                          A signed count of real lines is interpreted as
                          some lattice root enumeration, which lets us
                          prove our invariance properties for del Pezzo
                          of degree 1 and 2, like in the case of cubic
                          surfaces.<br>
                        </font></font></div>
                    <div align="left"><font color="#ff0000"><font
                          color="#000000"><br>
                        </font></font></div>
                    <div align="left"><font color="#ff0000"><font
                          color="#000000"><b><font color="#ff0000">Date:<font
                                color="#000000"> 5 November 2021</font></font></b>,
                          Friday</font></font><br>
                    </div>
                    <div align="left"><font color="#ff0000"><font
                          color="#000000"><b> <font color="#ff0000">Time:
                            </font>15:40 (GMT+3)</b><br>
                          <b><font color="#ff0000">Place: </font></b><font
                            color="#ff0000"><font color="#000000"><b>Zoom<br>
                              </b></font></font></font></font></div>
                    <div align="left"><font color="#ff0000"><font
                          color="#000000"><font color="#ff0000"><font
                              color="#000000"><b><br>
                              </b></font></font></font></font></div>
                    <blockquote>
                      <p><font color="#ff0000"><font color="#000000"><font
                              color="#ff0000"><font color="#000000"><b><b
style="color:rgb(51,51,51);font-family:arial,verdana,sans-serif;font-size:14px">One
                                    day before the seminar, an
                                    announcement with the Zoom meeting
                                    link will be sent to those who
                                    registered with Sertöz. <br>
                                  </b></b></font></font></font></font></p>
                      <p><font color="#ff0000"><font color="#000000"><font
                              color="#ff0000"><font color="#000000"><b><b
style="color:rgb(51,51,51);font-family:arial,verdana,sans-serif;font-size:14px">If
                                    you have registered before for one
                                    of the previous talks, there is no
                                    need to register again; you will
                                    automatically receive a link for
                                    this talk too.<br>
                                  </b></b></font></font></font></font></p>
                      <p><font color="#ff0000"><font color="#000000"><font
                              color="#ff0000"><font color="#000000"><b><b
style="color:rgb(51,51,51);font-family:arial,verdana,sans-serif;font-size:14px">If
                                    you have not registered before,
                                    please contact him at <a
href="mailto:sertoz@bilkent.edu.tr?subject=Zoom%20Seminar%20Address%20Request"
                                      target="_blank">sertoz@bilkent.edu.tr</a>.</b></b></font></font></font></font></p>
                    </blockquote>
                    <p><font color="#ff0000"><font color="#000000"><font
                            color="#ff0000"><font color="#000000"><b> </b></font></font></font></font></p>
                    <div align="left"><br>
                    </div>
                    <div align="left">Please bring your own tea and
                      cookies and  self-serve at the convenience of your
                      own home! 😁<span></span></div>
                    <div align="left"><br>
                    </div>
                    <div align="left">You are most cordially invited to
                      attend.</div>
                    <div align="left"><br>
                    </div>
                    <div align="left">Ali Sinan Sertöz<br>
                      <font color="#ff0000"><font color="#000000"><b><font
                              color="#ff0000"> </font></b></font></font></div>
                    <pre cols="72"><div style="text-align:left"><span style="font-family:Arial,Helvetica,sans-serif">------------------------------</span><span style="font-family:Arial,Helvetica,sans-serif">------------------------------</span><span style="font-family:Arial,Helvetica,sans-serif">---------------- </span></div><div style="text-align:left"><span style="font-family:Arial,Helvetica,sans-serif">Ali Sinan Sertöz</span></div><div style="text-align:left"><span style="font-family:Arial,Helvetica,sans-serif">Bilkent University, Department of Mathematics, 06800 Ankara, Turkey</span></div><div style="text-align:left"><span style="font-family:Arial,Helvetica,sans-serif">Office: (90)-(312) - 290 1490</span></div><div style="text-align:left"><span style="font-family:Arial,Helvetica,sans-serif">Department: (90)-(312) - 266 4377</span></div><div style="text-align:left"><span style="font-family:Arial,Helvetica,sans-serif">Fax: (90)-(312) - 290 1797</span></div><div style="text-align:left"><span style="font-family:Arial,Helvetica,sans-serif">e-mail: </span><a href="mailto:sertoz@bilkent.edu.tr" style="font-family:Arial,Helvetica,sans-serif" target="_blank" class="moz-txt-link-freetext">sertoz@bilkent.edu.tr</a><span style="font-family:Arial,Helvetica,sans-serif"> </span></div><div style="text-align:left"><span style="font-family:Arial,Helvetica,sans-serif">Web: </span><a href="http://sertoz.bilkent.edu.tr" style="font-family:Arial,Helvetica,sans-serif" target="_blank">sertoz.bilkent.edu.tr</a><span style="font-family:Arial,Helvetica,sans-serif"> </span></div><div style="text-align:left"><span style="font-family:Arial,Helvetica,sans-serif">------------------------------</span><span style="font-family:Arial,Helvetica,sans-serif">------------------------------</span><span style="font-family:Arial,Helvetica,sans-serif">----------------</span></div></pre>
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