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Proposition: Prop. 9.21: Sum of Even Numbers is Even

(Proposition 21 from Book 9 of Euclid's “Elements”)

If any multitude whatsoever of even numbers is added together then the whole is even.

• For let any multitude whatsoever of even numbers, $AB$, $BC$, $CD$, $DE$, lie together.
• I say that the whole, $AE$, is even.

Modern Formulation

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Table of Contents

Proofs: 1

Mentioned in:

Proofs: 1 2 3

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References

Adapted from (subject to copyright, with kind permission)

1. Fitzpatrick, Richard: Euclid's "Elements of Geometry"

Adapted from CC BY-SA 3.0 Sources:

1. Prime.mover and others: "Pr∞fWiki", https://proofwiki.org/wiki/Main_Page, 2016