we may obtain further results. If we wish to know what is the term not-B, we have as before, by the Law of Duality,
b = Ab ꖌ ab
and substituting for A we obtain
b = Bb ꖌ ab = ab.
But we may now also draw a second contrapositive; for we have
a = aB ꖌ ab,
and substituting for B its equivalent A we have
a = aA ꖌ ab = ab.
Hence from the single identity A = B we can draw the two propositions
a = ab
b = ab,