Power bank and electric fan: what they have in common

1. Step 1. Power bank — has part — Lithium-ion battery. A battery.
2. Step 2. Lithium-ion battery — is part of — Robot vacuum. A battery.
3. Step 3. Robot vacuum — evolved from — Vacuum cleaner. An autonomous vacuum cleaner.
4. Step 4. Vacuum cleaner — has part — Impeller. An impeller creates the suction.
5. Step 5. Impeller — is part of — Electric fan. A fan's blades are an impeller that pushes the air.

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