Reflex hammer and watt steam engine: what they have in common

1. Step 1. Reflex hammer — is a kind of — Hammer. A hammer.
2. Step 2. Hammer — evolved into — Steam hammer. A steam hammer is a hammer lifted by steam, used to forge huge parts.
3. Step 3. Steam hammer — has part — Cylinder. A steam cylinder.
4. Step 4. Cylinder — is part of — Watt steam engine. Steam works in the cylinder.

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