P(TH) is both for S1 and S2. You can treat TH/TT/HT/HH as four different cases. In each diffrent case, you oberseve different S1 and S2.
One example: You can treat St as the Stock price at time t. And treat H as \”good market\” and T as \”bad market\”. Then HH means both two time (time 1 and time 2) are \”good market\”.
