1988 IMO Problems/Problem 2
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Problem
Let be a positive integer and let
be subsets of a set
.
Suppose that
(a) Each has exactly
elements,
(b) Each
contains exactly one element, and
(c) Every element of belongs to at least two of the
.
For which values of can one assign to every element of
one of the numbers
and
in such a way that
has
assigned to exactly
of its elements?