Aircraft and chisel: what they have in common

1. Step 1. Aircraft — includes — Hot air balloon. A balloon.
2. Step 2. Hot air balloon — has part — Gas burner. It heats the air in the envelope with a propane flame.
3. Step 3. Gas burner — is part of — Gas lamp. A coal-gas burner.
4. Step 4. Gas lamp — evolved into — Street light. Gas lamps.
5. Step 5. Street light — is part of — Tunnel. Lighting.
6. Step 6. Tunnel — uses — Chisel. Hezekiah’s Tunnel was cut by hand with chisels.

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