Suppose we have a constraint satisfaction problem that can be defined as its constraints in two different viewpoints $V_1$ and $V_2$. Moreover, there are two variables $A$ and $B$ from $V_1$ and $V_2$ respectively, such that the value $I$ for the variable $A$ in $V_1$ is equivalent to value $J$ for the variable $B$ in $V_2$. Now the question is how we can define the channeling constraint in CHR if we choose $V_1$ to solve the problem? Is it enough to write $P_1(A,I) ==> P_2(B,J)$? (suppose $P1$ and $P2$ are two predicates related to their viewpoints).
However, this propagation in the context of CHR does not help to solve the problem more efficient as we have no constraints over the variables of $V_2$.
Notice that this question in the matter of programming asked here but not solved yet.