Square paper bag bottom and vacuum pump: what they have in common

1. Step 1. Square paper bag bottom — is part of — Paper bag. Margaret Knight’s rectangular bottom.
2. Step 2. Paper bag — evolved into — Plastic bag. A replacement for paper.
3. Step 3. Plastic bag — is made of — Polyethylene. Polyethylene.
4. Step 4. Polyethylene — is material for — Cling film. Polyethylene.
5. Step 5. Cling film — is used in — Vacuum sealer. Film.
6. Step 6. Vacuum sealer — has part — Vacuum pump. A pump.

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