By comparison, in previous work, both Unary-X and Reduce-L/R-X actions produce new labeled nodes (some of which are auxiliary nodes due to binarization).
our paradigm has two advantages: • it dramatically reduces the number of possible actions, from 3X + 1 or more in previous work to 3 + X, where X is the number of nonterminal labels, which we argue would simplify learning; • it does not require binarization (Zhu et al., 2013;Wang and Xue, 2014) or compression of unary chains (Mi and Huang, 2015) There is, however, a more closely-related "shiftproject-attach" paradigm by Henderson (2003).