Update: Please restrict your answers to "tweets" that give more than just the statement of the result, and give also the essence (or a useful hint) of the argument/novelty.
I am looking for examples that the essence of a notable mathematical development fits a tweet (140 characters in English, no fancy formulas).
Background and motivation: This question was motivated by some discussion with Lior Pachter and Dave Bacon (over Twitter). Going over my own papers and blog posts I found very few such examples. (I give one answer.) There were also few developments that I do not know how to tweet their essence but I feel that a good tweet can be made by a person with deep understanding of the matter.
I think that a good list of answers can serve as a good educational window for some developments and areas in mathematics and it won't be overly big.
At most 140 characters per answer, single link is permitted. Tweeting one's own result is encouraged.
Update: I learned quite a few things, and Noam's tweet that I accepted is mind-boggling.
Best Answer
Every rational r is xyz(x+y+z) for some rational x,y,z.
Proof: Euler (1749) found x(r),y(r),z(r). Nobody knows how.
I have a guess. http://www.math.harvard.edu/~elkies/euler_14t.pdf