On the Unique Game Conjecture by Subbash Knot https://cs.nyu.edu/~khot/papers/UGCSurvey.pdf

On Khot's Unique Game conjecture by Luca Trevisan https://www.ams.org/journals/bull/2012-49-01/S0273-0979-2011-01361-1/S0273-0979-2011-01361-1.pdf

Vertex Cover Might be Hard to Approximate within 2-e https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.123.4748&rep=rep1&type=pdf