Electrostatic state selector and gutenberg printing press: what they have in common

1. Step 1. Electrostatic state selector — is part of — Maser. It selects the excited molecules.
2. Step 2. Maser — evolved into — Laser. A laser is an optical maser.
3. Step 3. Laser — includes — Laser diode. A semiconductor laser.
4. Step 4. Laser diode — is part of — Laser printer. A laser draws the image on the drum.
5. Step 5. Laser printer — is a kind of — Printer. A printer.
6. Step 6. Printer — works like — Gutenberg printing press. A printer is a personal printing press: it transfers an image onto paper.

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