[Note that Rule (1) is merely the Formula expressed in words.]
Fig. II.
This includes any Pair of Premisses, of which one is a Nullity and the other an Entity, and which contain Like Eliminands.
The simplest case is
| xm0 † ym1 | |
 |  ∴ x′y1 |
In this case we see that the Conclusion is an Entity, and that the Nullity-Retinend has changed its Sign.
And we should find this Rule to hold good with any Pair of Premisses which fulfil the given conditions.
[The Reader had better satisfy himself of this, by working out, on Diagrams, several varieties, such as
x′m0 † ym1 (which ¶ xy1)
x1m′0 † y′m′1 (which ¶ x′y′1)
m1x0 † y′m1 (which ¶ x′y′1).]
The Formula, to be remembered, is,
xm0 † ym1 ¶ x′y1