this is the problem very difficult to solve

this is the problem very difficult to solveThis is the problem very difficult to solve.请问这句话的语法结构是什么呢?系动词引导的表语从句,那very difficult to solve充当什么成份?是不是相当于This is the problem which is difficult to solve.那哪些定语从句可以省略先行词？不是说在定语从句中,先行词在从句中做宾语,那么关系代词可以省略。