5th Book of Euclid. First definition: a part is a quantity of less
magnitude than the greater magnitude when the less is contained a
certain number of times in the greater.

A part properly speaking is that which may be multiplied, that is
when, being multiplied by a certain number, it forms exactly the
whole. A common aggregate part ...

Second definition. A greater magnitude is said to be a multiple of a
less, when the greater is measured by the less.

By the first we define the lesser [magnitude] and by the second the
greater is defined. A part is spoken