Due to the aforementioned conditions on the induced dependency tree, every arc that is added to T i−1 yields a set of lostArcs and lostParts that cannot be added to the partial tree in subsequent iterations.
the loss value is defined to be: every part that contains one or more arcs that violate the dependency tree conditions for a tree that extends the partial tree t i−1 ∪ {e} is considered a lost part as it will not be included in any tree extending t i−1 ∪{e}.