Note 29 — BOOK I. (continued 3)
Reading edition
If bx be substituted for a in any expression which is homogeneous with respect to a and b, the pupil may easily see that b must occur in every term as often as there are units in the degree of the expression: thus, aa + ab becomes bxbx + bxb or bb(xx + x); aaa + bbb becomes bxbxbx + bbb or bbb(xxx + 1); and so on.