Recent additions

26 Apr 2009
files added/renewed: solutions.html, pene16.pdf, pen.txt, new.html, index.html

• WARNING: Soon, this site will not be avaliable from http://www.oocities.org/de/darij_grinberg/ anymore.
  (The webhoster, Yahoo Geocities, appears to be closing down. When they have closed, my website will only be avaliable at http://www.cip.ifi.lmu.de/~grinberg/, until I have found a new webhoster.
  I am sorry for the inconvenience.)
• New solution added: Project PEN, problem E16.

16 Apr 2009
files added/renewed: solutions.html, O111.pdf, O112.pdf, O114.pdf, U111.pdf, U112.pdf, new.html, index.html

• New section: Solutions to review problems, already filled with some content (albeit not very spectacular).

6 Apr 2009
files added/renewed: index.html, new.html, Popoviciu.pdf, PopoviciuFormal.pdf, pen.txt, faq.html, subsetcond.pdf

• New note: Proof of a CWMO problem generalized.
• Generalizations of Popoviciu's inequality (both versions) updated with a reference to Theorem 6.
• FAQ updated.
• New problem published: Darij Grinberg, Cezar Lupu, Problem 896, College Mathematics Journal, 2009 no. 2 (March 2009).

18 Nov 2008
files added/renewed: index.html, new.html, pen.txt

• This site will soon disappear from http://www.stud.uni-muenchen.de/~darij.grinberg/ !
  Please change your links to http://www.cip.ifi.lmu.de/~grinberg/ .
  (The LMU is discontinuing to offer webspace for students on their servers. Fortunately, the Informatics Institute has its own hosting.)

20 Oct 2008
files added/renewed: index.html, new.html, Links.html, errata.html

• Updated the errata page with one more from Altshiller-Court.
• Link list slightly updated.

11 Oct 2008
files added/renewed: index.html, new.html, links.html, Dreigeom/Inhalt.html, Dreigeom/HBeckerBWM20062.zip

• Hanno Beckers Lösungen der 2. Runde des Bundeswettbewerbs Mathematik 2006 sind endlich lesbar - der Fehler lag auf meiner Seite.

13 Sep 2008 (ii)
files added/renewed: index.html, new.html, links.html, errata.html, errata1.html

• Updated the errata page.
• Link list updated due to the takedown of the Kalva site (check it out using the Wayback Machine). Whoever is responsible for the site going offline has earned a boo from the whole community...

13 Sep 2008 (i)
files added/renewed: index.html, new.html, CircumRev.pdf

• The note Circumscribed quadrilaterals revisited has been updated once again to include another theorem from MathLinks with a (new?) proof.

10 Sep 2008
files added/renewed: index.html, new.html, CircumRev.pdf

• The note Circumscribed quadrilaterals revisited has been updated to include some new material.
  To be honest, the new results are rather obvious; a more serious update may come soon.

23 Jul 2008
files added/renewed: index.html, new.html, pen.txt, NMMathesis.zip, Links.html

• Thanks to the help of Francisco Bellot Rosado, I have obtained the Mathésis article by V. Thébault and A. Mineur referenced as [6] in my article on The Neuberg-Mineur circle.
• PEN posts updated (inserted some new links).
• The link list was updated.

25 Mar 2008
files added/renewed: index.html, new.html, faq.html, errata.html, Popoviciu.pdf, PopoviciuFormal.pdf, pen.txt

• Generalizations of Popoviciu's inequality updated (corrected a linguistic mistake: in the formulations of Theorems 13 and 14, the word "assertion" could be misunderstood; now I have replaced it by "condition").
• PEN posts updated (inserted some new links).
• The errata page now also features Honsberger's book.

20 Mar 2008
files added/renewed: index.html, new.html, Popoviciu.pdf, PopoviciuFormal.pdf

• Generalizations of Popoviciu's inequality published on arXiv and added to this website.

14 Mar 2008
files added/renewed: index.html, new.html, StPeters2003.pdf

• Note edited: St. Petersburg 2003: An alternating sum of zero-sum subset numbers (put Lemmata 1-3 into the beginning; now it should be much less confusing).

13 Mar 2008
files added/renewed: index.html, new.html, faq.html, StPeters2003.pdf

• Note extended: St. Petersburg 2003: An alternating sum of zero-sum subset numbers (slightly restructured and Problem 2 added).
• FAQ updated.

15 Feb 2008
files added/renewed: index.html, new.html, faq.html, errata.html, StPeters2003.pdf

• Note added: St. Petersburg 2003: An alternating sum of zero-sum subset numbers.
• FAQ updated and an experimental page for errata in books created.

17 Dec 2007
files added/renewed: index.html, new.html, faq.html, O49.pdf

• New problem added: Cosmin Pohoata and Darij Grinberg, Problem F07-1, The Harvard College Mathematics Review, Vol. 1, No. 2, Fall 2007.
• FAQ updated: The public domain dedication contained some mistakes (both of spelling and of content).
• Proposed solution to Mathematical Reflections problem O49 added.

28 Nov 2007
files added/renewed: index.html, new.html, S64.pdf

• Proposed solution to problem S64 from Mathematical Reflections added.

31 Oct 2007
files added/renewed: index.html, new.html, QEDMOEnglish.zip

• The statements of the QEDMO problems in English updated: added problems of the 5th QEDMO.

6 Oct 2007
files added/renewed: index.html, new.html, Hall.pdf, HallAbridged.pdf

• Fixed two typos in An algebraic approach to Hall's matching theorem and in the abridged version of the same article.

5 Oct 2007
files added/renewed: index.html, new.html, Dreigeom/Inhalt.html, Dreigeom/Feuerbach.pdf, Dreigeom/Feuerbach.zip (removed), NewNinepoint/winkel.jpg, NewNinepoint/Feuer1.gif, NewNinepoint/Feuerbach.html

• Some more published problems added to the index.
• Edited the old note "New Insight on the Ninepoint Circle", fixing a mistake in the proof of Theorem 1. It is an outdated note anyway.
• Habe die Arbeit "Karl Wilhelm Feuerbach, sein Kreis und die Dreiecksgeometrie" erneuert. Alles, was ich dabei geändert habe, ist der Beweis von Satz 1, wo ich einen dummen Fehler verbessert habe. Bitte nicht wundern, daß die Arbeit eine Seite kürzer (habe den Rand verkleinert) und die PDF-Datei signifikant kleiner (habe sie mit einer neueren Ghostview-Version kompiliert) geworden ist.
• Liste der Veröffentlichungen in der WURZEL um ein paar Aufgaben ergänzt (alle die bis jetzt erschienen sind).

3 Oct 2007
files added/renewed: index.html, new.html, Links.html, Hall.pdf, HallAbridged.pdf, Dreigeom/HBeckerBWM20062.zip (removed), Dreigeom/SchlEG.pdf, Dreigeom/Inhalt.html

• Note added: An algebraic approach to Hall's matching theorem, with its abridged version.
• Habe meine alte Facharbeit "Schließungssätze in der ebenen Geometrie" auf Wunsch einiger Personen hin online gestellt.
• Hanno Beckers Lösungen zur 2. Runde vom BWM 2006 sind jetzt gelöscht, weil die ZIP-Datei defekt war (und der Autor seine Originalversion verloren hat).
• The link list was updated with a new German link.

26 Aug 2007
files added/renewed: index.html, new.html, O25.pdf, faq.html

• Proposed solution to Mathematical Reflections problem O25 is now online (but shouldn't be of any interest).

13 Aug 2007
files added/renewed: index.html, new.html, VornicuS.pdf, pen.txt, faq.html, QEDMOEnglish.zip

• New note: The Vornicu-Schur inequality and its variations. Not so new actually, but now it's open to everyone. :)
• PEN posts updated.
• The statements of the QEDMO problems in English edited (2nd and 4th QEDMO).
• FAQ updated with a reference to Nathan Altshiller-Court, College Geometry and reviews of two inequalities books.

9 Jul 2007
files added/renewed: index.html, new.html, faq.html, QEDMOEnglish.zip

• Now the archive with the the statements of the QEDMO problems in English contains all four QEDMO's organized so far.
• Added link to Problem O49.

28 Jun 2007
ALSO see 19 Jun 2007, 30 May 2007 and 9 Mar 2007 for server (3)
files added/renewed: index.html, new.html, faq.html, Dreigeom/Inhalt.html, DreiGeom/QEDMO4g.zip

• Die Lösungsbeispiele zu den Geometrieaufgaben der 4. QED-Mathematik-Olympiade sind da.
• Additions to FAQ.
• Finally the server (3) seems to work properly again.

19 Jun 2007
ALSO see 30 May 2007 and 9 Mar 2007 for server (3)
files added/renewed: index.html, new.html, GergonneEuler.pdf, me.html (removed), faq.html, pen.txt, QEDMOEnglish.zip

• Added note An unexpected application of the Gergonne-Euler theorem.
• Added a FAQ (and a few files related to it). I hope it is of help.

30 May 2007
ALSO see 9 Mar 2007 for servers (2) and (3)
files added/renewed: index.html, new.html, TPSymmedian.pdf, DreiGeom/Inhalt.html, NeubergMineur.pdf, DreiGeom/NeubergMineurDeutsch.pdf

• Added note The Neuberg-Mineur circle as well as its German version Der Neuberg-Mineurkreis.
• An article and a problem added to the list of publications.
• Minimal changes in Three properties of the symmedian point (fixed a typo).

9 Mar 2007
files added/renewed: index.html, new.html, DreiGeom/Inhalt.html, Dreigeom/QEDMO4a.zip

• Die Lösungsbeispiele zu den zwei Algebraaufgaben der 4. QED-Mathematik-Olympiade sind da - erstmal nur auf dem Geocities-Server. Geometrie wird in absehbarer Zukunft folgen.

16 Feb 2007
files added/renewed: index.html, new.html, BalticFeuer.zip, Butterfly.zip, ButterflyS.html
ALSO see 3 Feb 2007 for servers (2) and (3)

• New note: On cyclic quadrilaterals and the butterfly theorem.
• Added a copy of the paper From Baltic Way to Feuerbach - A Geometrical Excursion, published in Mathematical Reflections 2/2006 pages 1-20, to this site with some graphical errors fixed.
• Design of index page (hopefully) improved, along with the descriptions/abstracts of some notes.

3 Feb 2007
files added/renewed: index.html, new.html, links.html, NewNinepoint/Feuerbach.html, YiuSynth.zip, YiuSynthPDF.zip, YiuSynth/ (directory removed), SymmedianPedal.zip, SymmedianPedalPDF.zip, SymmedianPedal/ (directory removed), ComplexCos.pdf

• New note: Two problems on complex cosines.
• The link list now contains a whole section of links to internet libraries.
• the URLs should now be changed).

29 Dec 2006
files added/renewed: index.html, new.html, links.html, me.html, CircumRev.pdf, Dreigeom\Inhalt.html, Schroeder\Schroeder.html

• Circumscribed quadrilaterals revisited has been unsubstantially edited (references to MathLinks topics have changed because of merging topics).
• Shortcuts added to index.html. Hope they are of help. Some minor updates to the rest of the site (in most cases, descriptions for various stuff were made more understandable).

23 Sep 2006
files added/renewed: index.html, new.html, Isogonal.pdf, Isogonal.zip

• Isogonal conjugation with respect to a triangle has now been extended. Because of problems with compilation, I had to put some of the graphics in an extra file, so the whole is in a ZIP archive now.

9 Sep 2006
files added/renewed: index.html, new.html, Dreigeom\Inhalt.html, Dreigeom\HBeckerBWM20062.zip, Dreigeom\DHarrerBWM_Runde2_2006.zip

• Hanno Beckers und Daniel Harrers Lösungen der 2. Runde des Bundeswettbewerbs Mathematik 2006 sind hoch.

8 Sep 2006
files added/renewed: index.html, new.html, Isogonal.pdf, Dreigeom\Inhalt.html, Dreigeom\200602.zip

• Added a reference to Isogonal conjugation with respect to a triangle.
• Die Lösungen der 2. Runde des Bundeswettbewerbs Mathematik 2006 sind da. (Und ich kann euch versichern, ihr wollt sie nicht sehen. Har har har.)

3 Sep 2006
files added/renewed: index.html, new.html, Dreigeom\QEDMO3g.pdf

• Die Lösungsbeispiele zu den Geometrieaufgaben der 3. QED-Mathematik-Olympiade wurden um einen Satz 3 c) bei Aufgabe G2 ergänzt. Die inkorrekt dargestellten Zeichnungen zu Aufgabe G2 wurden aus der Lösungs-PDF entfernt (jetzt sind sie nur noch in der zweiten PDF zu finden).

1 Sep 2006
files added/renewed: index.html, new.html, Isogonal.pdf, Dreigeom\Inhalt.html, Dreigeom\QEDMO3g.pdf

• Die Lösungsbeispiele zu den Geometrieaufgaben der 3. QED-Mathematik-Olympiade sind da.
• Fixed minor bugs in Isogonal conjugation with respect to a triangle (for some mystical reason, the segment PQ disappeared each time Fig. 13 was compiled - making the segment dashed stopped this strange behaviour; also, corrected a misspelling of my name in the list of references :) ).

28 Aug 2006

• Lösungsbeispiele zu den Algebraaufgaben der 3. QED-Mathematik-Olympiade leicht ergänzt (dritter Beweis von (A1.1) bei Aufgabe A1 hinzugefügt). Die Geometrieaufgaben werden in absehbarer Zeit folgen.
• Die Lösungen der 2. Runde des Bundeswettbewerbs Mathematik 2006 sind fertig und werden 1 Woche nach Einsendeschluss (1. September 2006) hochgestellt. Dies wird auch die letzte Runde des BWM sein, an der ich teilnehme.
• Minor updates throughout the site, mostly in the links section.

• Change of official email address! [19 Jan 2006]
  My new email address is
  AB=gmail.com
  where the letter A should be replaced by darij
  the letter B should be replaced by grinberg
  and the sign = by the sign @.
  The old address (which ends with web.de) is dead. Please don't send mails there; the amount of spam makes it impossible for me to filter out the good mail.

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Darij Grinberg