as pointed out by many authors, the mechanism by which the amounts of the two envelopes are determined is crucial for the decision of the player to switch or not his/her envelope. suppose that the amounts in the two envelopes a and b were not determined by first fixing contents of two envelopes e1 and e2, and then naming them a and b at random (for instance, by the toss of a fair coin; nickerson and falk, 2006). instead, we start right at the beginning by putting some amount in envelope a, and then fill b in a way which depends both on chance (the toss of a coin) and on what we put in a. suppose that first of all the amount "a" in envelope a is fixed in some way or other, and then the amount in envelope b is fixed, dependent on what is already in a, according to the outcome of a fair coin. ιf the coin fell heads then 2"a" is put in envelope b, if the coin fell tails then "a"/2 is put in envelope b. if the player was aware of this mechanism, and knows that they hold envelope a, but don't know the outcome of the coin toss, and doesn't know "a", then the switching argument is correct and he/she is recommended to switch envelopes. this version of the problem was introduced by nalebuff (1988) and is often called the ali-baba problem. notice that there is no need to look in envelope a in order to decide whether or not to switch.