EN
We consider the problem of the vanishing of non-negative continuous solutions ψ of the functional inequalities
(1) ψ(f(x)) ≤ β(x,ψ(x))
and
(2) α(x,ψ(x)) ≤ ψ(f(x)) ≤ β(x,ψ(x)),
where x varies in a fixed real interval I. As a consequence we obtain some results on the uniqueness of continuous solutions φ :I → Y of the equation
(3) φ(f(x)) = g(x,φ(x)),
where Y denotes an arbitrary metric space.