Book spine and laser: what they have in common

1. Step 1. Book spine — is part of — Codex (book). Sewing the signatures together.
2. Step 2. Codex (book) — is used in — Gutenberg printing press. The press printed sheets that were bound into codex books.
3. Step 3. Gutenberg printing press — works like — Printer. A printer is a personal printing press: it transfers an image onto paper.
4. Step 4. Printer — includes — Laser printer. A printer.
5. Step 5. Laser printer — has part — Laser diode. A laser draws the image on the drum.
6. Step 6. Laser diode — is a kind of — Laser. A semiconductor laser.

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