  In this article, we propose a new classification of $\Sigma^0_2$ formulas
under the realizability interpretation of many-one reducibility (i.e., Levin
reducibility). For example, ${\sf Fin}$, the decision of being eventually zero
for sequences, is many-one/Levin complete among $\Sigma^0_2$ formulas of the
form $\exists n\forall m\geq n.\varphi(m,x)$, where $\varphi$ is decidable. The
decision of boundedness for sequences ${\sf BddSeq}$ and for width of posets
${\sf FinWidth}$ are many-one/Levin complete among $\Sigma^0_2$ formulas of the
form $\exists n\forall m\geq n\forall k.\varphi(m,k,x)$, where $\varphi$ is
decidable. However, unlike the classical many-one reducibility, none of the
above is $\Sigma^0_2$-complete. The decision of non-density of linear order
${\sf NonDense}$ is truly $\Sigma^0_2$-complete.
