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ISL 1988 Problem 46

    A1,A2,…,A29A_1, A_2, \ldots, A_{29} are 2929 different sequences of positive integers. For 1≤i<j≤291 \leq i < j \leq 29 and any natural number x,x, we define Ni(x)=N_i(x) = number of elements of the sequence AiA_i which are less or equal to x,x, and Nij(x)=N_{ij}(x) = number of elements of the intersection Ai∩AjA_i \cap A_j which are less than or equal to x.x. It is given for all 1≤i≤291 \leq i \leq 29 and every natural number x,x, Ni(x)≥xe,N_i(x) \geq \frac{x}{e}, where e=2.71828…e = 2.71828 \ldots Prove that there exist at least one pair i,ji,j ( 1≤i<j≤291 \leq i < j \leq 29 ) such that Nij(1988)>200.N_{ij}(1988) > 200.

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