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Imagine a mug with this picture on its side:
This picture shows three houses and three utilities: gas (G), electricity (E), and water (W). Connect each house to all three utilities with paths that do not cross each other.
[Note] In the picture below, all three houses are connected to gas, but the house on the left is not connected to electricity or water. So this is incorrect.
This puzzle appears in 3Blue1Brown’s video Why this puzzle is impossible. It is known as the Three utilities problem.