Space under floor on brick pillars and elevator: what they have in common

1. Step 1. Space under floor on brick pillars — is part of — Hypocaust. A space under the floor on brick pillars.
2. Step 2. Hypocaust — evolved into — Central heating. The Roman hypocaust was an early central heating system.
3. Step 3. Central heating — has part — Boiler. A boiler.
4. Step 4. Boiler — is made of — Wrought iron. Later — made of sheet wrought iron.
5. Step 5. Wrought iron — is material for — Elevator safety brake. The safety catches are wrought iron.
6. Step 6. Elevator safety brake — is part of — Elevator. Otis’s safety brakes.

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