2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/99383The ideal anti-Zeno effect means that a perpetual observation leads to an immediate disappearance of the unstable system. We present a straightforward way to derive sufficient conditions under which such a situation occurs expressed in terms of the decaying states and spectral properties of the Hamiltonian. They show, in particular, that the gap between Zeno and anti-Zeno effects is in fact very narrow.LatEx2e, 9 pages; a revised text, to appear in J. Phys. A: Math. GenQuantum PhysicsMathematical Physicstext