Railway signal lamp and knife: what they have in common

1. Step 1. Railway signal lamp — is part of — Railway semaphore. A night signal.
2. Step 2. Railway semaphore — uses — Lever. The semaphore is set by a lever.
3. Step 3. Lever — is used in — Chopsticks. A third-class lever.
4. Step 4. Chopsticks — is a kind of — Cutlery. Chopsticks are East Asian cutlery.
5. Step 5. Cutlery — has part — Knife. Knives.

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