Show that if A1, A2, . . . , An are sets where n ≥ 2, and for all pairs of integers i and j with 1 ≤ i < j ≤ n either Ai is a subset of Aj or Aj is a subset of Ai, then there is an integer i, 1 ≤ i ≤ n such that Ai is a subset of Aj for all integers j with 1 ≤ j ≤ n.