  We elaborate on the notion of rectification of a Boolean classifier $\Sigma$.
Given $\Sigma$ and some background knowledge $T$, postulates characterizing the
way $\Sigma$ must be changed into a new classifier $\Sigma \star T$ that
complies with $T$ have already been presented. We focus here on the specific
case of mono-label Boolean classifiers, i.e., there is a single target concept
and any instance is classified either as positive (an element of the concept),
or as negative (an element of the complementary concept). In this specific
case, our main contribution is twofold: (1) we show that there is a unique
rectification operator $\star$ satisfying the postulates, and (2) when $\Sigma$
and $T$ are Boolean circuits, we show how a classification circuit equivalent
to $\Sigma \star T$ can be computed in time linear in the size of $\Sigma$ and
$T$; when $\Sigma$ and $T$ are decision trees, a decision tree equivalent to
$\Sigma \star T$ can be computed in time polynomial in the size of $\Sigma$ and
$T$.
