\noindent{}Determining whether a \constraint{} has to be \gls{reified} is a crucial decision made during \gls{rewriting}.
\minizinc{} allows us to write complex \constraints{} that in the process of \gls{rewriting} result in multiple \constraints{} that reason about each other.
However, using a \gls{reif} \(b \leftrightarrow{} c\), that determines whether a \constraint{} \(c\) holds, can slow the \solver{} down.
Even in \gls{cp} \solvers{}, few \glspl{reif} are \gls{native} to the \solvers{}, and the \glspl{propagator}, for the ones that are, are often weak.
Generally, the \glspl{decomp} of \gls{reified} \constraints{} also result in numerous \gls{native} \constraints{} and \variables{}.
It is thus important that \gls{rewriting} avoids the use of \gls{reif}, whenever it is not required.
 
In this chapter we present an extended \gls{reif} analysis to help minimize the required \solver{} effort.
Not only does it consider if a \constraint{} must be \gls{reified} or not, but it also considers whether it could instead be \gls{half-reified}.

The notion of \gls{half-reif} \(b \rightarrow{} c\) for a \constraint{} \(c\) was introduced by \textcite{feydy-2011-half-reif}.
They show that \gls{half-reif} can mitigate some problems and expenses of the use of \gls{reif}.
It is not always possible, however, to use a \gls{half-reif} instead of a \gls{reif}.
They also identify the conditions required for its usage and provide an algorithm that rewrites a subset of the \minizinc{} language using the technique.
Crucially, because of the omission of \gls{let} and multiple occurrences of identifiers, this algorithm does not directly generalize to the full \minizinc{} language.
This chapter re-evaluates \gls{half-reif} and extends the \gls{rewriting} process to fully support \gls{half-reif} in \minizinc{}.

This chapter is organized as follows.
In \cref{sec:half-intro,sec:half-propagation} we introduce the core concepts of \gls{half-reif} and \glspl{propagator} for \gls{half-reified} \constraints{}, as discussed by \textcite{feydy-2011-half-reif}.
\Cref{sec:half-decomposition} shows the benefits of \gls{half-reif} when writing \glspl{decomp} for \gls{mip} and \gls{sat} \solvers{}.
In \cref{sec:half-context} we introduce our new context analysis algorithm: a way to determine where \gls{half-reif} can be used in \microzinc{}, and by extension \minizinc{}.
Then, in \cref{sec:half-rewriting}, we elaborate on how using \gls{half-reif} changes the \gls{rewriting} process.
Finally, the effects of \glspl{propagator} for \gls{half-reified} \constraints{} and the introduction of \gls{half-reif} is analysed in \cref{sec:half-experiments}.
