As -----as or so----as=="as"or "so" is an adverb to modify an adjective and then followed by " as" which acts as a conjunctive. For example: It's not so difficult as I expected. In the case of comparisons of equality,in the patterns :as x adj. or adv.x as, not so x adj or adv. x as: For example; I want a box twice as large as this. It isn't so(as) big as you think it is. Yip
According to the dictionary.