{0}

All the possible positions of the value {1} in the {2} are in the same {3}. Because the {2} must contain the value {1}, the {3} will have the value {1} in one of the intersecting cells.

Hence other possible positions of the value {1} that are in the {3} but not in the {2} can be removed.

Therefore we can remove {4}.

{5}