For those who have really difficult time to understand this... I find <a href="http:&#x2F;&#x2F;news.sciencemag.org&#x2F;math&#x2F;2015&#x2F;11&#x2F;mathematician-claims-breakthrough-complexity-theory" rel="nofollow">http:&#x2F;&#x2F;news.sciencemag.org&#x2F;math&#x2F;2015&#x2F;11&#x2F;mathematician-claims...</a> opens a small door. I still have tons of questions, probably due to my failure of completing my complexity class in undergraduate.