LIGO and submarine: what they have in common

1. Step 1. LIGO — uses — Laser. A laser.
2. Step 2. Laser — has part — Mirror. A resonator made of mirrors.
3. Step 3. Mirror — is part of — Periscope. Mirrors or prisms.
4. Step 4. Periscope — is part of — Submarine. A periscope.

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