MathDB
Finite game on coordinate plane, nut's game

Source: Kazakhstan National Olympiad 2024 (10-11 grade), P4

March 21, 2024
analytic geometrycombinatorics

Problem Statement

Players AA and BB play the following game on the coordinate plane. Player AA hides a nut at one of the points with integer coordinates, and player BB tries to find this hidden nut. In one move BB can choose three different points with integer coordinates, then AA tells whether these three points together with the nut's point lie on the same circle or not. Can BB be guaranteed to find the nut in a finite number of moves?