Leather book binding and sewage treatment plant: what they have in common

1. Step 1. Leather book binding — is part of — Codex (book). Boards covered with leather.
2. Step 2. Codex (book) — is made of — Paper. Later ones were made of paper.
3. Step 3. Paper — is material for — Rocket. The first rockets were paper tubes filled with gunpowder.
4. Step 4. Rocket — is used in — Launch complex. Launching rockets.
5. Step 5. Launch complex — is made of — Concrete. The launch table is concrete.
6. Step 6. Concrete — is material for — Sewage treatment plant. The tanks are concrete.

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