Proof: By Euclid
(related to Proposition: Prop. 9.33: Number whose Half is Odd is Even-Times Odd)
- For let the number $A$ have an odd half.
- I say that $A$ is an even-times-odd (number) only.
Adapted from (subject to copyright, with kind permission)
- Fitzpatrick, Richard: Euclid's "Elements of Geometry"