In scenarios 2 and 3, Peter calculates the probability that DSM pulls ahead by one or two blocks "in some future" given that DSM find a block with probability of q and other miners find one with probability of p (p+q=1). According to Peter, DSM pulls ahead by one block with probability of q/p and by two blocks with probability of (q/p)^2. This is completely wrong! To see the mistake, we can do

reductio ad absurdum