The puzzle for this issue is in a different vein. A man wishes to generate a random sequence of 0's and 1's with the two digits equally likely. That is, in each position 0 and 1 occur with probability 1/2. Note that this does not imply that there must be an equal number of 0's and 1's in the string, only that they were generated via a process that made each equally likely to occur. For example, one method would be to obtain a fair coin, flip it repeatedly, and let each head be "0" and tail be "1". Now suppose that you have a coin, but you suspect that it may not be fair. The puzzle is to find a procedure using only the (possibly biased) coin that is guaranteed to generate a sequence with 0's and 1's equally likely. You may assume that neither heads nor tails have probability 0 for the biased coin.