IQ problem? (Come in, master)

There are two people, one is lying and the other is telling the truth. Set two boxes a and b, one with and one without.

Then you ask A, "Which box did B say the baby was in?"

If A answers "B says the baby is in box A", then the baby is in box B.

If A answers "B says the baby is in box B", then the baby is in box A.

The principle is: it is known that two mutually exclusive propositions p, q.p and q can take 0 or 1, 1 as true and 0 as false, so no matter who is true or false, pq=0 is affirmative.