Two updates on the EGMO textbook

Posted on by Evan Chen (陳誼廷)

Couple Thanksgiving presents for y’all:

Errata List now on GitHub

  • The list of errata is now version controlled on GitHub: https://github.com/vEnhance/egmo-book-errata.
    So now you can actually see a changelog of the ocean of typos as they come in.

    Shout-out to the crew working on the Japanese translation of the book for finding way more errors than I will ever care to admit (I didn’t count, but it’s probably in the 200-300 ballpark).

Automatically Generated EGMO Solutions Treasury (AGEST)

  • I took a snapshot my database entries for sourced problems in EGMO.
    It turns out that I have many written up already, so we now have something of a solutions manual for about half the problems or so.
    Since I like idiotic names, I dubbed it the Automatically Generated EGMO Solutions Treasury.

    You can download it here: https://web.evanchen.cc/upload/AGEST.pdf
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Published by Evan Chen (陳誼廷)

Evan is a math olympiad coach who completed his number theory PhD at MIT.

5 thoughts on “Two updates on the EGMO textbook”

  1. In the book, I found a proof of the first part of lemma 4.33, can you tell me if this is correct?If you observe, the setup is purely projective so you can use a projective transformation to send the circle to itself and K to the centre of the circle(O). This sends T to T’, A to A’ and B to B’. Then it is trivial that T’O intersects the circle the arc midpoint of A’B’, and hence we are done

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      2. Suppose you take a homography fixing the large circle and sending K to the center. The smaller circle is no longer necessarily a circle after the transformation (in general, it could be any ellipse); and the image of M’ is no longer necessarily the midpoint of arc A’B’.

        At the risk of being blunt, if you thought Lemma 4.33 was purely projective then you definitely should re-read section 9.7 of the textbook (or perhaps skip it for now and come back in several months when you have more experience).

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