Ex-3.38

;Ex-3.38 a
Without interleaving there are 6(Fact(3) ways in which they can do their transactions) cases possible.

1. Peter, Paul, Mary .. balance: $45
2. Paul, Peter, Mary .. balance: $45
3. Peter, Mary, Paul .. balance: $35
4. Paul, Mary, Peter .. balance: $50
5. Mary, Peter, Paul .. balance: $40
6. Mary, Paul, Peter .. balance: $40

;Ex-3.38b
deposit/withdraw of Peter/Paul can be divided in 2 steps
(set! balance (+/ balance amt))
1. Access the current balance
2. Calculating (+/- balance amt) and setting balance to the calculated value.

Let us denote these 2 steps for both person's transactions as Peter-1, Peter-2, and Paul-1, Paul-2.

withdraw of Mary can be divided in 3 steps
(set! balance (- balance (/ balance 2)))
Mary-1: Access the balance for calculating (/ balance 2)
Mary-2: Access the balance for calculating (- balance (/..
Mary-3: Setting balance to value calculated in step Mary-2


One of the possible execution sequence could be....

Peter-1 Paul-1 Mary-1 Peter-2 Paul-2 Mary-2 Mary-3

..with this sequence the final balance would be... $30