Observe also that the set of actions differs from the standard top down formulation of RNNG (Dyer et al., 2016) and from the inorder transition system of (Liu and Zhang, 2017) only because of the definition of the Open action: our formulation pops from the stack the left corner constituent S 0 and pushes back on the stack the predicted category •N before S 0 .
during parsing, the stack keeps the same internal structure as in the top down version (Dyer et al., 2016) but the tree traversal is different.