On the Subject of Coinage
Spoiler warning for “The Impossible Chessboard Puzzle”.
There are 64 coins, in an 8×8 grid, each either heads or tails.
 Take the serial number, and replace each character with a 1 if it’s within 5–9 or N–Z, and a 0
otherwise. Call this the hamming code.
 Next, create another 6digit code. Start by counting the number of heads in the highlighted
(black) region in the 1st table. If the sum is even, the 1st digit is 0, otherwise 1. Repeat the
above for the other 5 tables to obtain 5 more digits, which gives you the 6digit
code.
 To solve the module, press the coin in which—when flippedwill make both 6digit codes the
same. Flipping an incorrect coin gives a strike.
1st 
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2nd 
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3rd 
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5th 
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 Take the hamming code and the code generated from the module and generate a new 6bit sequence. For each position, set it to a 1 if the corresponding positions in both codes are different, and 0 otherwise.
 Take the first 3 bits of the sequence in this table to obtain the correct column.
1st  0  1 
2nd  0  1  0  1 
3rd  0  1  0  1  0  1  0  1 
 a  e  c  g  b  f  d  h 
 Take the last 3 bits of the sequence in this table to obtain the correct row.
4th  0  1 
5th  0  1  0  1 
6th  0  1  0  1  0  1  0  1 
 8  4  6  2  7  3  5  1 
 Flip the coin at this coordinate.