IMO 2024 Shortlist A7

Let Q be the set of rational numbers. Let f : Q Ñ Q be a function such that the following property holds: for all x, y P...

IMO 2024 Shortlist A7

Category: Algebra

Problem

Let Q be the set of rational numbers. Let f : Q Ñ Q be a function such that the following property holds: for all x, y P Q, fpx fpyqq “ fpxq y or fpfpxq yq “ x fpyq. Determine the maximum possible number of elements of tfpxq ` fp´xq | x P Qu. (Japan) 4 Bath, United Kingdom, 10th –22nd July 2024