Shoe heel and sonar: what they have in common

1. Step 1. Shoe heel — is part of — Footwear. A heel.
2. Step 2. Footwear — is made of — Leather. Leather.
3. Step 3. Leather — is material for — Submarine. It was covered with leather.
4. Step 4. Submarine — has part — Sonar. Underwater acoustics.

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