Pulley and gas lamp: what they have in common

1. Step 1. Pulley — uses — Rope. A rope runs over the pulley.
2. Step 2. Rope — is made of — Plant fibre. Rope is twisted from plant fibres.
3. Step 3. Plant fibre — is material for — Wick. A wick is twisted from plant fibres.
4. Step 4. Wick — is part of — Oil lamp. The wick feeds oil to the flame.
5. Step 5. Oil lamp — evolved into — Incandescent light bulb. The electric lamp replaced oil and gas lamps.
6. Step 6. Incandescent light bulb — evolved from — Gas lamp. Electricity displaced gas lighting.

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