Stadium and telescope: what they have in common

1. Step 1. Stadium — has part — Street light. Floodlights.
2. Step 2. Street light — has part — LED. LEDs.
3. Step 3. LED — is part of — Traffic light. LEDs.
4. Step 4. Traffic light — evolved from — Railway semaphore. The first traffic light was a railway-style semaphore.
5. Step 5. Railway semaphore — evolved from — Optical telegraph. The semaphore idea.
6. Step 6. Optical telegraph — uses — Telescope. Signals were read through a telescope.

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