Six logicians stand one behind the other facing an opaque wall such that 2 are on one side and 4 are on the other. None of the logicians can turn around or see beyond the wall.
Each wears a black or white hat as shown below; "|" represents the wall, capital letters are used to identify the logicians, and "b" and "w" refer to black and white respectively.
b w | b w b w
A B | C D E F
Each knows the location of the others and the quantity of each colour of hat. Who will be first to declare having which colour?