Commentary on Proposition VII.15¶
Back to Proposition VII.15.
If there be four numbers $1, m, a, ma$ (such that $1$ measures $m$ the same number of times that $a$ measures $ma$), $1$ measures $a$ the same number of times that $m$ measures $ma$.
Except that the first number is unity and the numbers are said to measure instead of being a part of others, this proposition and its proof do not differ from VII. 9; in fact this proposition is a particular case of the other.