Sufficiency
lTo show that a given set of gate types is sufficient, it
is enough to show that and, or, and not can be realized with those gate types.
lActually it is sufficient to show just and and not can
be realized, since or can
be realized as:
a + b = (aÕ bÕ)Õ
by DeMorganÕs law. So if and and not are realizable, so is or.