For each potential new lexicon Λ , NEW-LEX computes the probability p(y * |x i , z i ; θ , Λ ) of the original parse y * under Λ and parameters θ that are the same as θ but have weights for the new lexical items, as described in Section 7.
if the learned lexical items are used in too many incorrect parses, the stochastic gradient updates will down weight them to the point where the lexical induction step can merge or re-split nodes in the trees that contain them.