Online Resources:
+ AOPS Community, Contest Collections for the IMO: https://artofproblemsolving.com/community/c3222_imo
+ IMO Official Page: https://www.imo-official.org/problems.aspx
Books:
+ Djukic, et al. (2011) The IMO Compendium 1959-2009, Springer, 2nd edition.
+ Greitzer (1978), International Mathematical Olympiads 1959-1977, Mathematical Association of America (MAA).
+ Klamkin (1986), International Mathematical Olympiads 1978-1985, Mathematical Association of America (MAA).
+ Kuczma (2000), International Mathematical Olympiads 1986-1999, Mathematical Association of America (MAA).
