Cartesian coordinates and steam locomotive: what they have in common

1. Step 1. Cartesian coordinates — uses — Euclidean geometry. Analytic geometry.
2. Step 2. Euclidean geometry — is used in — Armillary sphere. The rings model the celestial circles.
3. Step 3. Armillary sphere — has part — Axle. The celestial axis.
4. Step 4. Axle — is part of — Wheelset. A common axle.
5. Step 5. Wheelset — has part — Flanged wheel. Two flanged wheels.
6. Step 6. Flanged wheel — is part of — Steam locomotive. Flanged wheels keep it on the track.

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