IMO Shortlist 1988 problem 10
Dodao/la: arhiva2. travnja 2012.
is said to be separating, if for every pair
there is a set
contains just one element.
is said to be covering, if every element of
is contained in at least one set
What is the smallest value
so there is a set
which is simultaneously separating and covering?
Izvor: Međunarodna matematička olimpijada, shortlist 1988