An explicit evaluation of these two competing requests shows that it is inappropriate, without taking into account this basic fact, to deal with the actual occurrence and emergence of Zeno's effect. Closely related (and sometimes not distinguished from the quantum Zeno effect) is the "watchdog effect", in which the time evolution of a system is affected by its continuous coupling to the environment. Unstable quantum systems are predicted to exhibit a short-time deviation from the exponential decay law. This universal phenomenon has led to the prediction that frequent measurements during this nonexponential period could inhibit decay of the system, one form of the quantum Zeno effect. Subsequently, it was predicted that measurements applied more slowly could also "enhance" decay rates, a phenomenon known as the quantum anti-Zeno effect. In quantum mechanics, the interaction mentioned is called "measurement" because its result can be interpreted in terms of classical mechanics. Frequent measurement prohibits the transition. It can be a transition of a particle from one half-space to another (which could be used for an atomic mirror in an atomic nanoscope) as in the time-of-arrival problem, a transition of a photon in a waveguide from one mode to another, and it can be a transition of an atom from one quantum state to another. It can be a transition from the subspace without decoherent loss of a qubit to a state with a qubit lost in a quantum computer. In this sense, for the qubit correction, it is sufficient to determine whether the decoherence has already occurred or not. All these can be considered as applications of the Zeno effect. By its nature, the effect appears only in systems with distinguishable quantum states, and hence is inapplicable to classical phenomena and macroscopic bodies. The mathematician Robin Gandy recalled Turing's formulation of the quantum Zeno effect in a letter to fellow mathematician Max Newman, shortly after Turing's death:  As a result of Turing's suggestion, the quantum Zeno effect is also sometimes known as the "Turing paradox". The idea is implicit in the early work of John von Neumann on the mathematical foundations of quantum mechanics, and in particular the rule sometimes called the "reduction postulate". It was later shown that the quantum Zeno effect of a single system is equivalent to the indetermination of the quantum state of a single system. The treatment of the Zeno effect as a paradox is not limited to the processes of quantum decay. In general, the term "Zeno effect" is applied to various transitions, and sometimes these transitions may be very different from a mere "decay" (whether exponential or non-exponential).