Shaduf and heat pump: what they have in common

1. Step 1. Shaduf — is used in — Well. Or with a well sweep.
2. Step 2. Well — is made of — Stone. The walls of wells were lined with stone.
3. Step 3. Stone — is material for — Ice house. Ice houses were built of stone and sunk into the ground.
4. Step 4. Ice house — evolved into — Refrigerator. The refrigerator replaced natural ice.
5. Step 5. Refrigerator — works like — Heat pump. A heat pump is a refrigerator that heats the house.

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