, whence the values of the moduli are
so that the expansion (9) gives
which is in fact only another form of (11a). We have, then, by the Rule
the former implies that there are no Xs which are not-Ys, the latter that there are no Ys which are not-Xs, these together expressing the full significance of the original equation.
We can, however, often recombine the constituents with a gain of simplicity. In the present instance, subtracting (12) from (11b), we have
or