 Misra and Sudarshan (1977) proposed to make the concept of “continual monitoring” precise using a Zeno-like supertask. Imagine that an unstable atom is evolving according to some law of unitary evolution \(U_t\). Suppose we measure whether or not the atom has decayed by following that regressive form of Zeno’s Dichotomy above. Namely, we measure it at time \(t\), but also at time \(t/2\), and before that at time \(t/4\), and at time \(t/8\), and so on. Let \(E\) be a projection corresponding to the initial undecayed state of the particle. Finding the atom undecayed at each stage in the supertask then corresponds to the sequence,