We now have a Tumblr: Tumblr: http://numberphile.tumblr.com This paper on ebay: http://www.ebay.co.uk/itm/221197137799? Just how hard was the second problem cracked by Will in Good Will Hunting? Matt Damon! And who doesn't love Homeomorphically Irreducible Trees? This video features Dr James Grime - http://singingbanana.com/ Music by Alan Stewart - http://www.youtube.com/user/AlanKey86 Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets: https://twitter.com/numberphile Google Plus: http://bit.ly/numberGplus Tumblr: http://numberphile.tumblr.com Videos by Brady Haran Brady's other channels include: http://www.youtube.com/periodicvideos (Chemistry stuff) http://www.youtube.com/sixtysymbols (Physics and astronomy) http://www.youtube.com/numberphile (Numbers and maths) http://www.youtube.com/DeepSkyVideos (Space stuff) http://www.youtube.com/nottinghamscience (Science and behind the scenes) http://www.youtube.com/foodskey (Food science) http://www.youtube.com/BackstageScience (Big science facilities) http://www.youtube.com/favscientist (Favourite scientists) http://www.youtube.com/bibledex (Academic look at the Bible) http://www.youtube.com/wordsoftheworld (Modern language and culture) http://www.youtube.com/PhilosophyFile (Philosophy stuff) http://www.youtube.com/PsyFile (Psychology stuff)