==> logic/smullyan/stamps.p <==
The moderator takes a set of 8 stamps, 4 red and 4 green, known to the
logicians, and loosely affixes two to the forehead of each logician so that
each logician can see all the other stamps except those 2 in the moderator's
pocket and the two on her own head.  He asks them in turn
if they know the colors of their own stamps:
  A: "No"
  B: "No"
  C: "No"
  A: "No
  B: "Yes"
  What are the colors of her stamps, and what is the situation?