Proposition: 7.38: Divisor is Reciprocal of Divisor of Integer
(Proposition 38 from Book 7 of Euclid's “Elements”)
If a number has any part whatever then it will be measured by a number called the same as the part.
 For let the number $A$ have any part whatever, $B$.
 And let the [number] $C$ be called the same as the part $B$ (i.e., $B$ is the $C$th part of $A$).
 I say that $C$ measures $A$.
Modern Formulation
If $\frac AC=B$ for some natural number $B,$ then $A$ is a multiple of $C.$
Table of Contents
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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