Track circuit and laser: what they have in common

1. Step 1. Track circuit — uses — Electrical conduction. The wheelset closes the circuit.
2. Step 2. Electrical conduction — is used in — Silver. The best conductor.
3. Step 3. Silver — is material for — Mirror. A silver coating.
4. Step 4. Mirror — is part of — Laser. A resonator made of mirrors.

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