De institutione musica II.10: Qui ex multiplicibus et superparticularibus multiplicatis fiant.
This also seems to be put first, which will be demonstrated a little later: if a multiple interval is multiplied by two, that which is born of that multiplication is also multiple; but if that which is begotten of such a multiplication is not multiple, then that which was multiplied by two is not multiple. Likewise, if a superparticular proportion is multiplied by two, that which results is neither superparticular nor multiple. And if that which is born of such a multiplication is neither multiple nor superparticular, then that which has been multiplied by two is superparticular or of another kind, but not multiple.