This paper is well written and can be used as a good example for training paper-writing skills. The way they wrote the introduction is fantastic and arguably clear. Although reviewers might come up with a lot of negative comments in the very beginning when everything sounds like so "bully", they will eventually convinced by their discussions about the question and its solution in a story-line. To be honest, I like this paper, especially the introduction section.
It is worth to read the proof in great details, but we will left to the future to save time.
