IMO Shortlist 1987 problem 17
Dodao/la: arhiva2. travnja 2012.
Prove that there exists a four-coloring of the set
such that any arithmetic progression with
terms in the set
is not monochromatic.
. Prove that there is a function
that is not constant on every set of
that form an arithmetic progression.
Proposed by Romania
Izvor: Međunarodna matematička olimpijada, shortlist 1987