Definition: 7.14: Not Coprime Numbers
And numbers composite to one another are those (which are) measured by some number as a common measure.
Modern Formulation
Negation of coprime, formally,
\[a\not\perp b\Longleftrightarrow\gcd(a,b) > 1.\]
Mentioned in:
Proofs: 1
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References
Adapted from (subject to copyright, with kind permission)
 Fitzpatrick, Richard: Euclid's "Elements of Geometry"
Adapted from CC BYSA 3.0 Sources:
 Prime.mover and others: "Pr∞fWiki", https://proofwiki.org/wiki/Main_Page, 2016