A moderator takes a set of 8 stamps, 4 red and 4 green, known to three logicians, and affixes two to the forehead of each logician so that each logician can see all the other stamps except those two in the moderator's pocket and the two on his or her own head. He asks them in turn if they know the colors of their own stamps:
1. A: "No"
2. B: "No"
3. C: "No"
4. A: "No"
5. B: "Yes"
What are the colors of B's stamps?
The first time around B does not know what colors he has. So
obviously, A and C do not have all four of one color. And also
since B knows that neither A or C know what colors they have, B then
knows that not all four colors are showing for either of them.
The only way B could know the second time around, without A knowing is
if A and B had two of the same color, but different, and he had one of
each. If A or B had one of each, then B could not know what he
has.
My solution
