18 dominoes in 6x6 board (Chile NMO 1991 P3)
Source:
November 20, 2021
Tilingtilescombinatorics
Problem Statement
A board of is totally covered by dominoes (of ), that is, there are no overlaps, gaps, and the tiles do not come off the board. Prove that, regardless of the arrangement of the tiles, there is always a line that divides the board into two non-empty parts, and without cutting tiles.