A1,A2,…,A29 are 29 different sequences of positive integers. For 1≤i<j≤29 and any natural number x, we define Ni(x)= number of elements of the sequence Ai which are less or equal to x, and Nij(x)= number of elements of the intersection Ai∩Aj which are less than or equal to x. It is given for all 1≤i≤29 and every natural number x, Ni(x)≥ex, where e=2.71828… Prove that there exist at least one pair i,j (1≤i<j≤29) such that Nij(1988)>200. combinatorics unsolvedcombinatorics