Sawdust and laser: what they have in common

1. Step 1. Sawdust — is material for — Ice house. Thermal insulation of the ice.
2. Step 2. Ice house — evolved into — Refrigerator. The refrigerator replaced natural ice.
3. Step 3. Refrigerator — uses — Refrigerant. A refrigerant.
4. Step 4. Refrigerant — is made of — Ammonia. Ammonia was one of the first refrigerants.
5. Step 5. Ammonia — is material for — Maser. The first maser ran on ammonia.
6. Step 6. Maser — evolved into — Laser. A laser is an optical maser.

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