| Is it possible to fill each square of a 5x5 grid with either a 1 or a 0, such that every 2x2 square is unique? The example has one repeated square. |

Source: Original. Found later as a color-map question in Aaron J.
Friedland's book __Puzzles in Math & Logic__ (New York, 1970) on pages 9-10
and 44.

Solution

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