“…The latter is defined in terms of creation, annihilation, and number operators, a † = f (N b )b † , a = bf (N b ), N = N b , satisfying the commutation relations [17,18,19,20] N, a † = a † , [N, a] = −a, a, a † = G(N), (1.2) where f is some Hermitian operator-valued function of the number operator and G(N) = (N + 1)f 2 (N + 1) − Nf 2 (N). Nonlinear CS defined as eigenstates of a [18,20,21,22,23], of a 2 [24], or of an arbitrary power a λ (λ > 2) [25] have, for instance, been considered in connection with nonclassical properties.…”