Idea: Prune values from a domain that are not in a list distributor's list

[pvdz]

I don't think this is done yet but the list distributor, that is a variable that is defined with an ordered list of values to attempt, should remove any value from its domain that is not in the list. In fact, it should be the intersection of its initial domain and the values in the list.

Symmetrically the list could be pruned from values not in the initial domain.

Should first check whether this is actually useful at all. Maybe list vars are already defined "cleanly" in our system.

Note that if the var contains a backup distributor, the above trick can not be applied since non-list values in the domain may still be valid. Just only after the list has been exhausted. The list itself could still be updated to remove values not in the initial domain.