有关集合的探索性问题,是一类条件不明确或结论不确定的集合问题,需要对题目中提供的各种信息进行观察、概括、猜想,从中探索、寻觅问题所需要的条件或判定结论是否成立,必要时还需要给出严格的证明.例1设M、P是两个非空集合,定义M与P的差集为:M-P={x|x∈M且x P},则M-(M-P)等于 The exploratory problem of collections is a set of problems with unclear conditions or inconclusive conclusions. It is necessary to observe, generalize, and conjecture various kinds of information provided in the questions, and to find out whether the conditions or judgments required for the problems are to be found or sought out. Set up, if necessary, also need to give a rigorous proof. Example 1 Let M, P is a non-empty set of two, define the difference between M and P is: MP = {x | x ∈ M and x P}, then M- (MP) is equal to