Sasha playing with knights...
Source: Tuymaada 2007, Problem 7
July 15, 2007
geometryrectangleanalytic geometrycombinatorics proposedcombinatorics
Problem Statement
Several knights are arranged on an infinite chessboard. No square is attacked by more than one knight (in particular, a square occupied by a knight can be attacked by one knight but not by two). Sasha outlined a rectangle. What maximum number of knights can this rectangle contain?