elem.7.def.20

Numbers are proportional when the first is the same multiple, or the same part, or the same parts, of the second that the third is of the fourth.

Κύβος δὲ ὁ ἰσάκις ἴσος ἰσάκις ἢ [ ὁ ] ὑπὸ τριῶν ἴσων ἀριθμῶν περιεχόμενος.