This paper purports to prove that the ternary Goldbach conjecture, or Goldbach's weak conjecture, is true. It was released in 2013 but is still undergoing peer review. According to Wikipedia:

In 2013, Harald Helfgott released a proof of Goldbach's weak conjecture. As of 2018, the proof is widely accepted in the mathematics community, but it has not yet been published in a peer-reviewed journal. The proof was accepted for publication in the Annals of Mathematics Studies series in 2015, and has been undergoing further review and revision since; fully-refereed chapters in close to final form are being made public in the process.

This market resolves YES if the proof is published in a peer-reviewed journal with no error being found, and NO if a mistake is found in the proof. The close date will be extended if neither of these things happen by the listed date.