Giant Brains; or, Machines That Think

Table 7

Statement	Truth Value
not-P	1 - p
P and Q	pq
P or Q	p + q - pq
if P, then Q	1 - p + pq
P if and only if Q	1 - p - q + 2pq
P or else Q	p + q - 2pq

For example, suppose that we have two statements P and Q:

P: John Doe is eligible for insurance.

Q: John Doe requires a medical examination.

To test that the truth value of “P or Q” is p + q-pq, let us put down the four cases, and calculate the result (see Table 8).