  For each $f:[0,\infty)\to\Com$ formally consider its co-Poisson or M\"{u}ntz
transform $g(x)=\sum_{n\geq 1}f(nx)-\frac{1}{x}\int_0^\infty f(t)dt$. For
certain $f$'s with both $f, g \in L_2(0,\infty)$ it is true that the Riemann
hypothesis holds if and only if $f$ is in the $L_2$ closure of the vector space
generated by the dilations $g(kx)$, $k\in\Nat$. Such is the case for example
when $f=\chi_{(0,1]}$ where the above statement reduces to the strong Nyman
criterion already established by the author. In this note we show that the
necessity implication holds for any continuously differentiable function $f$
vanishing at infinity and satisfying $\int_0^\infty t|f'(t)|dt<\infty$. If in
addition $f$ is of compact support then the sufficiency implication also holds
true. It would be convenient to remove this compactness condition.
