Main rotor and saw: what they have in common

1. Step 1. Main rotor — is part of — Helicopter. A main rotor.
2. Step 2. Helicopter — has part — Gas turbine. A turboshaft engine.
3. Step 3. Gas turbine — has part — Turbine. A turbine.
4. Step 4. Turbine — evolved from — Water wheel. The water turbine evolved from the water wheel.
5. Step 5. Water wheel — is part of — Sawmill. Early sawmills were driven by water wheels.
6. Step 6. Sawmill — uses — Saw. The cutting tool is a saw.

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