JBMO Shortlist 2022 C3
Source: JBMO Shortlist 2022
June 26, 2023
combinatoricsJuniorBalkanshortlist
Problem Statement
There are boxes on the table. In the beginning, each of the boxes contains a positive integer (the integers are not necessarily distinct). Every minute, Alice makes one move. A move consists of the following. First, she picks a box which contains a number such that for some numbers and which are contained in some other boxes. Then she picks a positive integer . Finally, she removes from and replaces it with . If she cannot make any mobes, she stops. Prove that no matter how Alice makes her moves, she won't be able to make infinitely many moves.