Occasionally one of these, that one had thought was an extinct volcano, bursts into eruption in a surprising manner. It is much older than electric lighting, or even gas, but the new dress brings it up to date. The puzzle is to lay on water, gas, and electricity, from W, G and E, to each of the three houses, A, B and C, without any pipe crossing another. I, too, receive inquiries on a regular basis. Ensuing discussions reveal two distinct mindsets and two distinct approaches to the puzzle.
Some people see in it a construction site question of sorts.
Most of the people, however, feel that such an interpretation voids the puzzle of all mystery and surprise. They place 2 sets of three dots opposite each other thinking of each dot as either a utility installation or a house and try to connect the dots without crossings. For, if the implied question concerns a bipartite graph , then, as it follows from the elementary graph theory , the puzzle has no solution. To visualize a graph, nodes may be thought of as points in space, plane, or another surface, while edges are represented by curves connecting the nodes. Such modeling of a graph is not unique.