  In this paper, we study the counting functions $\psi_\mathcal{P}(x)$,
$N_\mathcal{P}(x)$ and $M_\mathcal{P}(x)$ of a generalized prime system
$\mathcal{N}$. Here $M_\mathcal{P}(x)$ is the partial sum of the M\"{o}bius
function over $\mathcal{N}$ not exceeding $x$. In particular, we study these
when they are asymptotically well-behaved, in the sense that $\psi_{\cal{P}}(x)
= x+O({x^{ \alpha+\epsilon }})$, $N_{\cal{P}}(x) = \rho x+O({x^{ \beta+\epsilon
}})$ and $ M_\mathcal{P}(x) = O(x^{\gamma+\epsilon})$, for some $\rho >0$ and
$\alpha, \beta, \gamma<1$. We show that the two largest of
$\alpha,\beta,\gamma$ must be equal and at least $\frac{1}{2}$.
