This is apparently not was intended, but I think it qualifies. From  [*Principia Mathematica*][1]: [the proof of 1+1=2][3] (I can't include the image bc I'm a new user, but perhaps an experienced user can edit this answer for me.)

  [1]: http://en.wikipedia.org/wiki/Principia_Mathematica
  [2]: http://en.wikipedia.org/wiki/File:Principia_Mathematica_theorem_54-43.png
  [3]: http://en.wikipedia.org/wiki/File:Principia_Mathematica_theorem_54-43.png