Ladder and railway semaphore: what they have in common

1. Step 1. Ladder — uses — Inclined plane. Climbing to a height.
2. Step 2. Inclined plane — is used in — Egyptian pyramid. According to a common hypothesis, the blocks were raised on ramps.
3. Step 3. Egyptian pyramid — uses — Lever. Levers were used to move the blocks.
4. Step 4. Lever — is used in — Railway semaphore. The semaphore is set by a lever.

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