Ambulance and vacuum pump: what they have in common

1. Step 1. Ambulance — has part — Ventilator. Medical equipment.
2. Step 2. Ventilator — has part — Valve. Valves.
3. Step 3. Valve — is part of — Boyle’s air pump. Valves.
4. Step 4. Boyle’s air pump — evolved from — Vacuum pump. An improved version of Guericke’s pump.

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