Random Time Change of a Martingale. Suppose that X is a martingale with respect to Ft and that {τt : t ≥ 0} is a no decreasing process of stopping times of Ft that are bounded a.s. Verify that X(τt)...

Random Time Change of a Martingale. Suppose that X is a martingale with respect to Ft and that {τt : t ≥ 0} is a no decreasing process of stopping times of Ft that are bounded a.s. Verify that X(τt) is a martingale with respect to Ft, and that its mean is E