| A = ABC ꖌ ABc, | (1) |
we know by the Law of Duality that
| AB = ABC ꖌ ABc. | (2) |
As the second member of this is identical with the second member of (1) we may substitute, obtaining
A = AB.
This process of reducing useless alternatives may be applied again and again; for it is plain that
A = AB (CD ꖌ Cd ꖌ cD ꖌ cd)
communicates no more information than that A is B. Abstraction of indifferent terms is in fact the converse process to that of development described in p. [89]; and it is one of the most important operations in the whole sphere of reasoning.
The reader should observe that in the proposition
AC = BC