First, make clear the definition and relationship between subset and proper subset. Definition of subset: (A and B are two sets) If any element in set A is an element in set B, then A is a subset of B; So if A is contained in B and A is not equal to B, then A is the proper subset of B. Any element is a subset of itself, so if there are n elements in the set R, there are 2 n subsets in the set R, including 2 n- 1 in proper subset.

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