When Ye Xiao arrived at the fourth floor, he could clearly feel that there was a layer of restriction in the library.
That type of restriction was mostly a type of array.
The so-called array was a special energy that was produced by using specially-refined ores that operate in a certain route.
That special energy had both offensive and defensive forms.
However, no matter which form it was, it could erupt with tremendous power.
The array was the protective umbrella of the high-level cultivation techniques hidden in the various areas, and it was also the first line of safety.
Therefore, it was usually contracted and built by the top array experts of the Nine Provinces Alliance.
That was also why, although Yang Zhengyi was a great grandmaster, he had no way of easily stealing the cultivation technique.
However, Ye Xiao had the director's approval, so he could easily enter the fourth floor.