2001 OIM Problems/Problem 3
Problem
Let 
be a set of 
elements and 
subsets of (
), such that each of them has at least 
elements. Show that 
and 
exist, with 
such that the number of common elements of 
and 
is greater than or equal to
![\[r-\frac{nk}{4(k-1)}\]](http://latex.artofproblemsolving.com/7/1/8/7186b9862ddea51503def6f463aecca38bab5edb.png)
~translated into English by Tomas Diaz. ~orders@tomasdiaz.com
Solution
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