Following Goldberg and Nivre 2013, we say that a set of arcs A is reachable from configuration c, written c A, if there is some (possibly empty) path of transitions from c to some configuration c = λ 1 , λ 2 , B, A , with A ⊆ A .
then, we can define the loss of a configuration as and the set of transitions that must be returned by a correct dynamic oracle is then i.e., the transitions that do not increase configuration loss, and hence lead to the best parse (in terms of loss) reachable from c. implementing a dynamic oracle reduces to computing the loss (c) for each configuration c. Goldberg and Nivre (2013) show that the calculation of the loss is easy for parsers that are arcdecomposable, i.e., those where for every configuration c and arc set A that is tree-compatible (i.e.