  Let $D(G)$ be the minimum quantifier depth of a first order sentence $\Phi$
that defines a graph $G$ up to isomorphism. Let $D_0(G)$ be the version of
$D(G)$ where we do not allow quantifier alternations in $\Phi$. Define $q_0(n)$
to be the minimum of $D_0(G)$ over all graphs $G$ of order $n$. We prove that
for all $n$ we have $\log^*n-\log^*\log^*n-1\le q_0(n)\le \log^*n+22$, where
$\log^*n$ is equal to the minimum number of iterations of the binary logarithm
needed to bring $n$ to 1 or below. The upper bound is obtained by constructing
special graphs with modular decomposition of very small depth.
