I am having trouble understanding why the following statement holds:
Consider a procedure which chooses a random odd number $n\leq x$ and then performs $k$ independent strong prime test on $n$ with bases drawn at random from $(1,n-1)$ Let $P_k(x)$ be the probability that this procedure accepts a composite number. Then:
$P_k(x)\leq \frac{4^{1-k}P_1(x)}{1-P_1(x)}$
I managed to derive a bound for $P_1(x)$ but that is all.